{"title":"Tropical paleobiology discovers biodiversity in a warmer past","authors":"Moriaki Yasuhara, C. Deutsch, Jingwen Zhang","doi":"10.1073/pnas.2404036121","DOIUrl":"https://doi.org/10.1073/pnas.2404036121","url":null,"abstract":"","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"671 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140776975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Correction to Supporting Information for Wiedmann et al., The material footprint of nations","authors":"","doi":"10.1073/pnas.2319720120","DOIUrl":"https://doi.org/10.1073/pnas.2319720120","url":null,"abstract":"","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"36 42","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138588812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Pullabhotla, Mustafa Zahid, S. Heft-Neal, Vaibhav Rathi, Marshall Burke
{"title":"Reply to Giglio and Roy: Aggregate infant mortality estimates robust to choice of burned area product","authors":"H. Pullabhotla, Mustafa Zahid, S. Heft-Neal, Vaibhav Rathi, Marshall Burke","doi":"10.1073/pnas.2318188120","DOIUrl":"https://doi.org/10.1073/pnas.2318188120","url":null,"abstract":"","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"54 35","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138593216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"FireCCILT11 artifacts may confound the link between biomass burning and infant mortality","authors":"Louis Giglio, David P. Roy","doi":"10.1073/pnas.2317759120","DOIUrl":"https://doi.org/10.1073/pnas.2317759120","url":null,"abstract":"","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"40 15","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138592392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-09DOI: 10.1101/2021.09.08.459427
R. Saecker, James Chen, C. Chiu, B. Malone, J. Sotiris, Mark Ebrahim, L. Y. Yen, E. Eng, S. Darst
Significance The modulation of the rate of formation and of the lifetime of transcription initiation complexes is a critical point in gene expression control. In Escherichia coli, single-nucleotide changes can change the half-life of an RNA polymerase (RNAP)–promoter DNA complex by more than an order of magnitude. The origins of these effects are poorly understood. Using cryoelectron microscopy, we find that small alterations in the sequence or size of the transcription bubble trigger global changes in RNAP–DNA interactions and in DNA base stacking. Our results reveal that nonadditive structural changes allow a few crucial DNA positions to tune the transcription initiation complex lifetime from seconds to hours, influencing the rate and efficiency of the initial steps of RNA synthesis. The first step in gene expression in all organisms requires opening the DNA duplex to expose one strand for templated RNA synthesis. In Escherichia coli, promoter DNA sequence fundamentally determines how fast the RNA polymerase (RNAP) forms “open” complexes (RPo), whether RPo persists for seconds or hours, and how quickly RNAP transitions from initiation to elongation. These rates control promoter strength in vivo, but their structural origins remain largely unknown. Here, we use cryoelectron microscopy to determine the structures of RPo formed de novo at three promoters with widely differing lifetimes at 37 °C: λPR (t1/2 ∼10 h), T7A1 (t1/2 ∼4 min), and a point mutant in λPR (λPR-5C) (t1/2 ∼2 h). Two distinct RPo conformers are populated at λPR, likely representing productive and unproductive forms of RPo observed in solution studies. We find that changes in the sequence and length of DNA in the transcription bubble just upstream of the start site (+1) globally alter the network of DNA–RNAP interactions, base stacking, and strand order in the single-stranded DNA of the transcription bubble; these differences propagate beyond the bubble to upstream and downstream DNA. After expanding the transcription bubble by one base (T7A1), the nontemplate strand “scrunches” inside the active site cleft; the template strand bulges outside the cleft at the upstream edge of the bubble. The structures illustrate how limited sequence changes trigger global alterations in the transcription bubble that modulate the RPo lifetime and affect the subsequent steps of the transcription cycle.
{"title":"Structural origins of Escherichia coli RNA polymerase open promoter complex stability","authors":"R. Saecker, James Chen, C. Chiu, B. Malone, J. Sotiris, Mark Ebrahim, L. Y. Yen, E. Eng, S. Darst","doi":"10.1101/2021.09.08.459427","DOIUrl":"https://doi.org/10.1101/2021.09.08.459427","url":null,"abstract":"Significance The modulation of the rate of formation and of the lifetime of transcription initiation complexes is a critical point in gene expression control. In Escherichia coli, single-nucleotide changes can change the half-life of an RNA polymerase (RNAP)–promoter DNA complex by more than an order of magnitude. The origins of these effects are poorly understood. Using cryoelectron microscopy, we find that small alterations in the sequence or size of the transcription bubble trigger global changes in RNAP–DNA interactions and in DNA base stacking. Our results reveal that nonadditive structural changes allow a few crucial DNA positions to tune the transcription initiation complex lifetime from seconds to hours, influencing the rate and efficiency of the initial steps of RNA synthesis. The first step in gene expression in all organisms requires opening the DNA duplex to expose one strand for templated RNA synthesis. In Escherichia coli, promoter DNA sequence fundamentally determines how fast the RNA polymerase (RNAP) forms “open” complexes (RPo), whether RPo persists for seconds or hours, and how quickly RNAP transitions from initiation to elongation. These rates control promoter strength in vivo, but their structural origins remain largely unknown. Here, we use cryoelectron microscopy to determine the structures of RPo formed de novo at three promoters with widely differing lifetimes at 37 °C: λPR (t1/2 ∼10 h), T7A1 (t1/2 ∼4 min), and a point mutant in λPR (λPR-5C) (t1/2 ∼2 h). Two distinct RPo conformers are populated at λPR, likely representing productive and unproductive forms of RPo observed in solution studies. We find that changes in the sequence and length of DNA in the transcription bubble just upstream of the start site (+1) globally alter the network of DNA–RNAP interactions, base stacking, and strand order in the single-stranded DNA of the transcription bubble; these differences propagate beyond the bubble to upstream and downstream DNA. After expanding the transcription bubble by one base (T7A1), the nontemplate strand “scrunches” inside the active site cleft; the template strand bulges outside the cleft at the upstream edge of the bubble. The structures illustrate how limited sequence changes trigger global alterations in the transcription bubble that modulate the RPo lifetime and affect the subsequent steps of the transcription cycle.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87841866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-08-20DOI: 10.1101/2021.08.20.457137
J. Bloch, S. Mukherjee, J. Kowal, E. Filippova, M. Niederer, E. Pardon, J. Steyaert, A. Kossiakoff, K. Locher
Significance Structural studies of membrane proteins by cryogenic electron microscopy (cryo-EM) often require antibody fragments (Fabs) to facilitate particle alignments and achieve high resolution. While conformational nanobodies have been developed to lock specific states of many membrane proteins, they only add 15 kDa of mass to the complex. We developed a synthetic Fab (NabFab) that rigidly binds the conserved scaffold of nanobodies, providing a universally applicable fiducial for cryo-EM studies of protein–nanobody complexes. We demonstrate the concept by determining two high-resolution structures of membrane proteins bound to specific nanobodies and NabFab. As the structural epitope for NabFab can be incorporated into the scaffold of virtually any nanobody, this raises the prospect of facile structure determination of many nanobody–protein complexes. With conformation-specific nanobodies being used for a wide range of structural, biochemical, and cell biological applications, there is a demand for antigen-binding fragments (Fabs) that specifically and tightly bind these nanobodies without disturbing the nanobody–target protein interaction. Here, we describe the development of a synthetic Fab (termed NabFab) that binds the scaffold of an alpaca-derived nanobody with picomolar affinity. We demonstrate that upon complementary-determining region grafting onto this parent nanobody scaffold, nanobodies recognizing diverse target proteins and derived from llama or camel can cross-react with NabFab without loss of affinity. Using NabFab as a fiducial and size enhancer (50 kDa), we determined the high-resolution cryogenic electron microscopy (cryo-EM) structures of nanobody-bound VcNorM and ScaDMT, both small membrane proteins of ∼50 kDa. Using an additional anti-Fab nanobody further facilitated reliable initial three-dimensional structure determination from small cryo-EM test datasets. Given that NabFab is of synthetic origin, is humanized, and can be conveniently expressed in Escherichia coli in large amounts, it may be useful not only for structural biology but also for biomedical applications.
{"title":"Development of a universal nanobody-binding Fab module for fiducial-assisted cryo-EM studies of membrane proteins","authors":"J. Bloch, S. Mukherjee, J. Kowal, E. Filippova, M. Niederer, E. Pardon, J. Steyaert, A. Kossiakoff, K. Locher","doi":"10.1101/2021.08.20.457137","DOIUrl":"https://doi.org/10.1101/2021.08.20.457137","url":null,"abstract":"Significance Structural studies of membrane proteins by cryogenic electron microscopy (cryo-EM) often require antibody fragments (Fabs) to facilitate particle alignments and achieve high resolution. While conformational nanobodies have been developed to lock specific states of many membrane proteins, they only add 15 kDa of mass to the complex. We developed a synthetic Fab (NabFab) that rigidly binds the conserved scaffold of nanobodies, providing a universally applicable fiducial for cryo-EM studies of protein–nanobody complexes. We demonstrate the concept by determining two high-resolution structures of membrane proteins bound to specific nanobodies and NabFab. As the structural epitope for NabFab can be incorporated into the scaffold of virtually any nanobody, this raises the prospect of facile structure determination of many nanobody–protein complexes. With conformation-specific nanobodies being used for a wide range of structural, biochemical, and cell biological applications, there is a demand for antigen-binding fragments (Fabs) that specifically and tightly bind these nanobodies without disturbing the nanobody–target protein interaction. Here, we describe the development of a synthetic Fab (termed NabFab) that binds the scaffold of an alpaca-derived nanobody with picomolar affinity. We demonstrate that upon complementary-determining region grafting onto this parent nanobody scaffold, nanobodies recognizing diverse target proteins and derived from llama or camel can cross-react with NabFab without loss of affinity. Using NabFab as a fiducial and size enhancer (50 kDa), we determined the high-resolution cryogenic electron microscopy (cryo-EM) structures of nanobody-bound VcNorM and ScaDMT, both small membrane proteins of ∼50 kDa. Using an additional anti-Fab nanobody further facilitated reliable initial three-dimensional structure determination from small cryo-EM test datasets. Given that NabFab is of synthetic origin, is humanized, and can be conveniently expressed in Escherichia coli in large amounts, it may be useful not only for structural biology but also for biomedical applications.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"83 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74514585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-08-19DOI: 10.1101/2021.08.19.456893
H. Deng, Yanying Xu, Xiaoyue Hu, Zhuang W. Zhen, Yuzhou Chang, Yewei Wang, A. Ntokou, M. Schwartz, Bing Su, M. Simons
Significance Inward remodeling of arteries to reduce lumen diameter is a major factor in disease progression and morbidity in multiple vascular diseases, including hypertension and atherosclerosis. However, molecular mechanisms controlling inward arterial remodeling remain largely undefined. In this study, we identify endothelial MEKK3 as an unexpected regulator of inward remodeling via inhibition of TGFβ-Smad2/3 signaling. Genetic deletion of MEKK3 in adult endothelium results in induction of TGFβ-Smad2/3 signaling, endothelial-to-mesenchymal transition, and inward remodeling in both pulmonary and arterial circuits. The latter process results in pulmonary and systemic hypertension and accelerates atherosclerosis. These results provide a basis for understanding the inward artery remodeling that leads to reduced blood flow to affected tissues and exacerbates hypertension in vascular disease. Arterial remodeling is an important adaptive mechanism that maintains normal fluid shear stress in a variety of physiologic and pathologic conditions. Inward remodeling, a process that leads to reduction in arterial diameter, plays a critical role in progression of such common diseases as hypertension and atherosclerosis. Yet, despite its pathogenic importance, molecular mechanisms controlling inward remodeling remain undefined. Mitogen-activated protein kinases (MAPKs) perform a number of functions ranging from control of proliferation to migration and cell-fate transitions. While the MAPK ERK1/2 signaling pathway has been extensively examined in the endothelium, less is known about the role of the MEKK3/ERK5 pathway in vascular remodeling. To better define the role played by this signaling cascade, we studied the effect of endothelial-specific deletion of its key upstream MAP3K, MEKK3, in adult mice. The gene’s deletion resulted in a gradual inward remodeling of both pulmonary and systematic arteries, leading to spontaneous hypertension in both vascular circuits and accelerated progression of atherosclerosis in hyperlipidemic mice. Molecular analysis revealed activation of TGFβ-signaling both in vitro and in vivo. Endothelial-specific TGFβR1 knockout prevented inward arterial remodeling in MEKK3 endothelial knockout mice. These data point to the unexpected participation of endothelial MEKK3 in regulation of TGFβR1-Smad2/3 signaling and inward arterial remodeling in artery diseases.
{"title":"MEKK3–TGFβ crosstalk regulates inward arterial remodeling","authors":"H. Deng, Yanying Xu, Xiaoyue Hu, Zhuang W. Zhen, Yuzhou Chang, Yewei Wang, A. Ntokou, M. Schwartz, Bing Su, M. Simons","doi":"10.1101/2021.08.19.456893","DOIUrl":"https://doi.org/10.1101/2021.08.19.456893","url":null,"abstract":"Significance Inward remodeling of arteries to reduce lumen diameter is a major factor in disease progression and morbidity in multiple vascular diseases, including hypertension and atherosclerosis. However, molecular mechanisms controlling inward arterial remodeling remain largely undefined. In this study, we identify endothelial MEKK3 as an unexpected regulator of inward remodeling via inhibition of TGFβ-Smad2/3 signaling. Genetic deletion of MEKK3 in adult endothelium results in induction of TGFβ-Smad2/3 signaling, endothelial-to-mesenchymal transition, and inward remodeling in both pulmonary and arterial circuits. The latter process results in pulmonary and systemic hypertension and accelerates atherosclerosis. These results provide a basis for understanding the inward artery remodeling that leads to reduced blood flow to affected tissues and exacerbates hypertension in vascular disease. Arterial remodeling is an important adaptive mechanism that maintains normal fluid shear stress in a variety of physiologic and pathologic conditions. Inward remodeling, a process that leads to reduction in arterial diameter, plays a critical role in progression of such common diseases as hypertension and atherosclerosis. Yet, despite its pathogenic importance, molecular mechanisms controlling inward remodeling remain undefined. Mitogen-activated protein kinases (MAPKs) perform a number of functions ranging from control of proliferation to migration and cell-fate transitions. While the MAPK ERK1/2 signaling pathway has been extensively examined in the endothelium, less is known about the role of the MEKK3/ERK5 pathway in vascular remodeling. To better define the role played by this signaling cascade, we studied the effect of endothelial-specific deletion of its key upstream MAP3K, MEKK3, in adult mice. The gene’s deletion resulted in a gradual inward remodeling of both pulmonary and systematic arteries, leading to spontaneous hypertension in both vascular circuits and accelerated progression of atherosclerosis in hyperlipidemic mice. Molecular analysis revealed activation of TGFβ-signaling both in vitro and in vivo. Endothelial-specific TGFβR1 knockout prevented inward arterial remodeling in MEKK3 endothelial knockout mice. These data point to the unexpected participation of endothelial MEKK3 in regulation of TGFβR1-Smad2/3 signaling and inward arterial remodeling in artery diseases.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75512317","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-08-19DOI: 10.1101/2021.08.19.457025
Xinyu Gu, Nicholas P. Schafer, P. Wolynes
Significance Messenger RNA (mRNA)/protein assemblies such as functional prions and condensates are involved in locally regulating translation in eukaryotic cells. The mode of regulation depends on the structure of these assemblies. We show that the vectorial processive nature of translation can couple to transport via diffusion so as to repress or activate translation depending on the structure of the RNA protein assembly. We find that multiple factors including diffusivity changes and free energy biases in the assemblies can regulate the translation rate of mRNA by changing the balance between substrate recycling and competition between mRNAs. We mainly focus on the example of CPEB, a functional prion that has been implicated in the mechanism of synaptic plasticity of neurons and in memory. Translation of messenger RNA (mRNA) is regulated through a diverse set of RNA-binding proteins. A significant fraction of RNA-binding proteins contains prion-like domains which form functional prions. This raises the question of how prions can play a role in translational control. Local control of translation in dendritic spines by prions has been invoked in the mechanism of synaptic plasticity and memory. We show how channeling through diffusion and processive translation cooperate in highly ordered mRNA/prion aggregates as well as in less ordered mRNA/protein condensates depending on their substructure. We show that the direction of translational control, whether it is repressive or activating, depends on the polarity of the mRNA distribution in mRNA/prion assemblies which determines whether vectorial channeling can enhance recycling of ribosomes. Our model also addresses the effect of changes of substrate concentration in assemblies that have been suggested previously to explain translational control by assemblies through the introduction of a potential of mean force biasing diffusion of ribosomes inside the assemblies. The results from the model are compared with the experimental data on translational control by two functional RNA-binding prions, CPEB involved in memory and Rim4 involved in gametogenesis.
{"title":"Vectorial channeling as a mechanism for translational control by functional prions and condensates","authors":"Xinyu Gu, Nicholas P. Schafer, P. Wolynes","doi":"10.1101/2021.08.19.457025","DOIUrl":"https://doi.org/10.1101/2021.08.19.457025","url":null,"abstract":"Significance Messenger RNA (mRNA)/protein assemblies such as functional prions and condensates are involved in locally regulating translation in eukaryotic cells. The mode of regulation depends on the structure of these assemblies. We show that the vectorial processive nature of translation can couple to transport via diffusion so as to repress or activate translation depending on the structure of the RNA protein assembly. We find that multiple factors including diffusivity changes and free energy biases in the assemblies can regulate the translation rate of mRNA by changing the balance between substrate recycling and competition between mRNAs. We mainly focus on the example of CPEB, a functional prion that has been implicated in the mechanism of synaptic plasticity of neurons and in memory. Translation of messenger RNA (mRNA) is regulated through a diverse set of RNA-binding proteins. A significant fraction of RNA-binding proteins contains prion-like domains which form functional prions. This raises the question of how prions can play a role in translational control. Local control of translation in dendritic spines by prions has been invoked in the mechanism of synaptic plasticity and memory. We show how channeling through diffusion and processive translation cooperate in highly ordered mRNA/prion aggregates as well as in less ordered mRNA/protein condensates depending on their substructure. We show that the direction of translational control, whether it is repressive or activating, depends on the polarity of the mRNA distribution in mRNA/prion assemblies which determines whether vectorial channeling can enhance recycling of ribosomes. Our model also addresses the effect of changes of substrate concentration in assemblies that have been suggested previously to explain translational control by assemblies through the introduction of a potential of mean force biasing diffusion of ribosomes inside the assemblies. The results from the model are compared with the experimental data on translational control by two functional RNA-binding prions, CPEB involved in memory and Rim4 involved in gametogenesis.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88571963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-08-16DOI: 10.1101/2021.08.16.456562
James R. Rybarski, Kuang Hu, A. Hill, C. Wilke, Ilya J. Finkelstein
Significance CRISPR-Cas systems confer bacteria and archaea with adaptive immunity against mobile genetic elements. These systems also participate in other cellular processes. For example, CRISPR-associated Tn7 transposons (CASTs) have co-opted nuclease-inactive CRISPR effector proteins to guide their transposition. We bioinformatically survey metagenomic databases to uncover CASTs, including systems with new architectures and ones that use distinct CRISPR subtypes. We also describe a putative non-Tn7 CAST that co-opts Cas12. Our findings propose mechanisms for vertical and horizontal CAST targeting and shed light on how CASTs have coevolved with CRISPR-Cas systems. CRISPR-associated Tn7 transposons (CASTs) co-opt cas genes for RNA-guided transposition. CASTs are exceedingly rare in genomic databases; recent surveys have reported Tn7-like transposons that co-opt Type I-F, I-B, and V-K CRISPR effectors. Here, we expand the diversity of reported CAST systems via a bioinformatic search of metagenomic databases. We discover architectures for all known CASTs, including arrangements of the Cascade effectors, target homing modalities, and minimal V-K systems. We also describe families of CASTs that have co-opted the Type I-C and Type IV CRISPR-Cas systems. Our search for non-Tn7 CASTs identifies putative candidates that include a nuclease dead Cas12. These systems shed light on how CRISPR systems have coevolved with transposases and expand the programmable gene-editing toolkit.
{"title":"Metagenomic discovery of CRISPR-associated transposons","authors":"James R. Rybarski, Kuang Hu, A. Hill, C. Wilke, Ilya J. Finkelstein","doi":"10.1101/2021.08.16.456562","DOIUrl":"https://doi.org/10.1101/2021.08.16.456562","url":null,"abstract":"Significance CRISPR-Cas systems confer bacteria and archaea with adaptive immunity against mobile genetic elements. These systems also participate in other cellular processes. For example, CRISPR-associated Tn7 transposons (CASTs) have co-opted nuclease-inactive CRISPR effector proteins to guide their transposition. We bioinformatically survey metagenomic databases to uncover CASTs, including systems with new architectures and ones that use distinct CRISPR subtypes. We also describe a putative non-Tn7 CAST that co-opts Cas12. Our findings propose mechanisms for vertical and horizontal CAST targeting and shed light on how CASTs have coevolved with CRISPR-Cas systems. CRISPR-associated Tn7 transposons (CASTs) co-opt cas genes for RNA-guided transposition. CASTs are exceedingly rare in genomic databases; recent surveys have reported Tn7-like transposons that co-opt Type I-F, I-B, and V-K CRISPR effectors. Here, we expand the diversity of reported CAST systems via a bioinformatic search of metagenomic databases. We discover architectures for all known CASTs, including arrangements of the Cascade effectors, target homing modalities, and minimal V-K systems. We also describe families of CASTs that have co-opted the Type I-C and Type IV CRISPR-Cas systems. Our search for non-Tn7 CASTs identifies putative candidates that include a nuclease dead Cas12. These systems shed light on how CRISPR systems have coevolved with transposases and expand the programmable gene-editing toolkit.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91324641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-07-20DOI: 10.1101/2021.07.19.452976
Chenghan Li, G. Voth
Significance As first proposed more than 200 y ago by Grotthuss, proton transport is enabled by a chemical bond-breaking and bond-making proton-hopping mechanism through water networks or “wires,” often contained within confined systems such as protein channels or nanotubes. Herein, concepts from graph theory are utilized in order to define a continuously differentiable collective variable for water wire connectivity and facile proton transport. As such, the water connectivity can be explicitly quantified via free-energy sampling to both qualitatively and quantitatively describe the thermodynamics and kinetics of water-facilitated proton transport via Grotthuss hopping—something that has been lacking since the first conceptual identification of this key chemical process in nature. Water-assisted proton transport through confined spaces influences many phenomena in biomolecular and nanomaterial systems. In such cases, the water molecules that fluctuate in the confined pathways provide the environment and the medium for the hydrated excess proton migration via Grotthuss shuttling. However, a definitive collective variable (CV) that accurately couples the hydration and the connectivity of the proton wire with the proton translocation has remained elusive. To address this important challenge—and thus to define a quantitative paradigm for facile proton transport in confined spaces—a CV is derived in this work from graph theory, which is verified to accurately describe water wire formation and breakage coupled to the proton translocation in carbon nanotubes and the Cl−/H+ antiporter protein, ClC-ec1. Significant alterations in the conformations and thermodynamics of water wires are uncovered after introducing an excess proton into them. Large barriers in the proton translocation free-energy profiles are found when water wires are defined to be disconnected according to the new CV, even though the pertinent confined space is still reasonably well hydrated and—by the simple measure of the mere existence of a water structure—the proton transport would have been predicted to be facile via that oversimplified measure. In this paradigm, however, the simple presence of water is not sufficient for inferring proton translocation, since an excess proton itself is able to drive hydration, and additionally, the water molecules themselves must be adequately connected to facilitate any successful proton transport.
{"title":"A quantitative paradigm for water-assisted proton transport through proteins and other confined spaces","authors":"Chenghan Li, G. Voth","doi":"10.1101/2021.07.19.452976","DOIUrl":"https://doi.org/10.1101/2021.07.19.452976","url":null,"abstract":"Significance As first proposed more than 200 y ago by Grotthuss, proton transport is enabled by a chemical bond-breaking and bond-making proton-hopping mechanism through water networks or “wires,” often contained within confined systems such as protein channels or nanotubes. Herein, concepts from graph theory are utilized in order to define a continuously differentiable collective variable for water wire connectivity and facile proton transport. As such, the water connectivity can be explicitly quantified via free-energy sampling to both qualitatively and quantitatively describe the thermodynamics and kinetics of water-facilitated proton transport via Grotthuss hopping—something that has been lacking since the first conceptual identification of this key chemical process in nature. Water-assisted proton transport through confined spaces influences many phenomena in biomolecular and nanomaterial systems. In such cases, the water molecules that fluctuate in the confined pathways provide the environment and the medium for the hydrated excess proton migration via Grotthuss shuttling. However, a definitive collective variable (CV) that accurately couples the hydration and the connectivity of the proton wire with the proton translocation has remained elusive. To address this important challenge—and thus to define a quantitative paradigm for facile proton transport in confined spaces—a CV is derived in this work from graph theory, which is verified to accurately describe water wire formation and breakage coupled to the proton translocation in carbon nanotubes and the Cl−/H+ antiporter protein, ClC-ec1. Significant alterations in the conformations and thermodynamics of water wires are uncovered after introducing an excess proton into them. Large barriers in the proton translocation free-energy profiles are found when water wires are defined to be disconnected according to the new CV, even though the pertinent confined space is still reasonably well hydrated and—by the simple measure of the mere existence of a water structure—the proton transport would have been predicted to be facile via that oversimplified measure. In this paradigm, however, the simple presence of water is not sufficient for inferring proton translocation, since an excess proton itself is able to drive hydration, and additionally, the water molecules themselves must be adequately connected to facilitate any successful proton transport.","PeriodicalId":20595,"journal":{"name":"Proceedings of the National Academy of Sciences","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85270598","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：