Molecular Cell最新文献

Oxidative phosphorylation (OXPHOS) fulfills energy metabolism and biosynthesis through the tricarboxylic acid (TCA) cycle and an intact electron transport chain (ETC). Mitochondrial glutamine import (MGI) replenishes the TCA cycle through glutaminolysis, but its broader roles in cancer remain unclear. Here, we show that MGI sustains OXPHOS independently of glutaminolysis by maintaining ETC integrity. Exogenous glutamate availability abrogates cellular dependence on glutaminolysis but not SLC1A5var-mediated MGI. Blocking MGI elicits severe mitochondrial defects, reducing mitochondrial glucose oxidation and increasing glutamine reductive carboxylation. MGI, but not glutaminolysis, is essential for mitochondrial translation by enabling biogenesis of Gln-mt-tRNA^Gln, the most limiting mitochondrial aminoacyl-tRNA in cancer cells. Finally, deleting SLC1A5 in mice and targeting SLC1A5var in xenograft tumors inhibit Gln-mt-tRNA^Gln biogenesis and mitochondrial translation and blunt tumor growth. Our findings uncover a previously unrecognized role of MGI in safeguarding ETC integrity independently of glutaminolysis and inform a therapeutic option by targeting MGI to abrogate OXPHOS for cancer treatment.

Mitochondria and the endoplasmic reticulum (ER) contain large areas that are in close proximity. Yet the mechanism of how these inter-organellar adhesions are formed remains elusive. Tight functional connections, termed "membrane contact sites," assemble at these areas and are essential for exchanging metabolites and lipids between the organelles. Recently, the ER-resident protein PDZ domain-containing protein 8 (PDZD8) was identified as a tether between the ER and mitochondria or late endosomes/lysosomes. Here, we show that PDZD8 can undergo phase separation via its intrinsically disordered region (IDR). Endogenously labeled PDZD8 forms condensates on membranes both in vitro and in mammalian cells. Electron microscopy analyses indicate that the expression of full-length PDZD8 rescues the decrease in inter-organelle contacts in PDZD8 knockout cells but not PDZD8 lacking its IDR. Together, this study identifies that PDZD8 condensates at the lipid interfaces act as an adhesive framework that stitches together the neighboring organelles and supports the structural and functional integrity of inter-organelle communication.

In this issue of Molecular Cell, Ishiguro et al.¹ describe new RNA modifications near the active site of the E. coli ribosome that appear only under anaerobic conditions. These modifications enhance ribosome activity and increase anaerobic growth rates.

In this issue of Molecular Cell, Zhu et al.¹ show that mitochondria of cancer cells rely on the import of glutamine not only to fuel metabolite synthesis via the tricarboxylic acid cycle but also to charge mt-tRNA^Gln to allow mitochondrial protein synthesis and respiration.

Approximately 10% of eukaryotic proteins are folded by the TRiC/CCT complex (TCP1-ring complex, also called CCT for cytosolic chaperonin containing TCP1), and only open-state TRiC can bind with programmed cell death 5 (PDCD5). However, the physiological role of the PDCD5-TRiC interaction remains elusive. Here, we show that PDCD5 is required for flagellum biogenesis and ciliogenesis and present the PDCD5-TRiC structures in their open states at near-atomic resolution. Mechanically, we find that PDCD5 promotes substrates release by competing with PhLP2A to interact with TRiC, and the depletion of PDCD5 traps flagellum- and cilium-associated proteins within TRiC, finally leading to malformed flagella of spermatids and cilia in mouse ciliated cells. Moreover, we demonstrate that the function of PDCD5 in flagellum biogenesis and ciliogenesis depends on the interaction with TRiC by its C terminus. These findings identify PDCD5 as a TRiC regulator to promote a subset of proteins release.

Members of the bromodomain and extraterminal domain (BET) protein family play a central role in transcription by RNA polymerase II (RNA Pol II). Small-molecule inhibitors that block interaction between BET bromodomains and acetylated histones have been developed for disease therapeutics. However, the BET protein BRD4 does not require bromodomains to perform its major transcriptional elongation control, and mechanisms by which other BET proteins regulate RNA Pol II remain insufficiently understood. Addressing the disparity between pan-BET degraders and BRD4-specific depletion, we report that the BET protein BRD2 generally functions to promote transcriptional initiation in a bromodomain-dependent manner at both promoters and enhancers in human cell lines. We demonstrate that BRD2 bromodomains preferentially bind to histone H4 harboring MOF-mediated H4K16ac, while the BRD2 C-terminal domain facilitates recruitment of TFIID. Our studies provide mechanistic insight into distinct roles for BRD2 and BRD4 in transcriptional initiation and elongation control for proper regulation of gene expression.

RNA-based anti-CRISPRs (Racrs) interfere with the type I-F CRISPR-Cas system by mimicking the repeats found in CRISPR arrays. Here, we determined the cryo-electron microscopy (cryo-EM) structures of the type I-F crRNA-guided surveillance complex (Csy complex) from Pectobacterium atrosepticum and three RacrIF1-induced aberrant subcomplexes. Additionally, we observed that Cas7f proteins could bind to non-specific nucleic acids, forming right-handed superhelical filaments composed of different Cas7 copies. Mechanistically, RacrIF1 lacks the specific S-conformation observed in the corresponding position of the 5' handle in canonical CRISPR complexes, and it instead adopts a periodic "5 + 1" pattern. This conformation creates severe steric hindrance for Cas5f-Cas8f heterodimer and undermines their binding. Furthermore, Cas7f nonspecifically binds nucleic acids and can form infinite superhelical filaments along Racrs molecules. This oligomerization sequesters Cas6f and Cas7f from binding, therefore blocking the formation of functional CRISPR-Cas effector complexes and ultimately blocking antiviral immunity. Our study provides a structural basis underlying Racrs-mediated CRISPRs inhibition.