Biochemical Society transactions最新文献

Membrane proteins play crucial roles in cellular functions. However, processes such as the insertion of membrane proteins into the endoplasmic reticulum (ER), their folding into native structures, the assembly of multi-subunit membrane protein complexes, and their targeting from the ER to specific organelles are prone to errors and have a relatively high failure rate. To prevent the accumulation of defective or orphaned membrane proteins, quality control mechanisms assess folding, quantity, and localization of these proteins. This quality control is vital for preserving organelle integrity and maintaining cellular health. In this mini-review, we will focus on how selective membrane protein quality control at the Golgi apparatus, particularly through the defective for SREBP cleavage (Dsc) ubiquitin ligase complex, detects orphaned proteins and prevents their mis-localization to other organelles.

Mammalian cells utilize over 1000 different lipid species to maintain cell and organelle membrane properties, control cell signaling and processes, and store energy. Lipid synthesis and metabolism are mediated by highly interconnected and spatiotemporally regulated networks of lipid-metabolizing enzymes and supported by vesicle trafficking and lipid-transfer at membrane contact sites. However, the regulatory mechanisms that achieve lipid homeostasis are largely unknown. Phosphatidic acid (PA) serves as the central hub for phospholipid biosynthesis, acting as a key intermediate in both the Kennedy pathway and the CDP-DAG pathway. Additionally, PA is a potent signaling molecule involved in various cellular processes. This dual role of PA, both as a critical intermediate in lipid biosynthesis and as a significant signaling molecule, suggests that it is tightly regulated within cells. This minireview will summarize the functional diversity of PA molecules based on their acyl tail structures and subcellular localization, highlighting recent tools and findings that shed light on how the physical, chemical, and spatial properties of PA species contribute to their differential metabolic fates and functions. Dysfunctional effects of altered PA metabolism as well as the strategies cells employ to maintain PA regulation and homeostasis will also be discussed. Furthermore, this review will explore the differential regulation of PA metabolism across distinct subcellular membranes. Our recent proximity labeling studies highlight the possibility that substrate cycling between PA and DAG may be location-dependent and have functional significance in cell signaling and lipid homeostasis.

Understanding of the physicochemical properties and functions of biomolecular condensates has rapidly advanced over the past decade. More recently, many RNA viruses have been shown to form cytoplasmic replication factories, or viroplasms, via phase separation of their components, akin to numerous cellular membraneless organelles. Notably, diverse viruses from the Reoviridae family containing 10-12 segmented double-stranded RNA genomes induce the formation of viroplasms in infected cells. Little is known about the inner workings of these membraneless cytoplasmic inclusions and how they may support stoichiometric RNA assembly in viruses with segmented RNA genomes, raising questions about the roles of phase separation in coordinating viral genome packaging. Here, we discuss how the molecular composition of viroplasms determines their properties, highlighting the interplay between RNA structure, RNA remodelling, and condensate self-organisation. Advancements in RNA structural probing and theoretical modelling of condensates can reveal the mechanisms through which these ribonucleoprotein complexes support the selective enrichment and stoichiometric assembly of distinct viral RNAs.

Advances in the study of mRNAs have yielded major new insights into post-transcriptional control of gene expression. Focus on the spatial regulation of mRNAs in highly polarized cells has demonstrated that mRNAs translocate through cells as mRNA:protein granules (mRNPs). These complex self-assemblies containing nuclear and cytoplasmic proteins are fundamental to the coordinated translation throughout cellular development. Initial studies on translational control necessitated fixed tissue, but the last 30 years have sparked innovative live-cell studies in several cell types to deliver a far more nuanced picture of how mRNA-protein dynamics exert translational control. In this review, we weave together the events that underpin mRNA processes and showcase the pivotal studies that revealed how a multitude of protein factors engage with a transcript. We highlight a mRNA's ability to act as a 'super scaffold' to facilitate molecular condensate formation and further moderate translational control. We focus on the Drosophila melanogaster germline due to the extensive post-transcriptional regulation occurring during early oogenesis. The complexity of the spatio-temporal expression of maternal transcripts in egg chambers allows for the exploration of a wide range of mechanisms that are crucial to the life cycle of mRNAs.

Voltage-clamp fluorometry (VCF) has revolutionized the study of ion channels by combining electrophysiology with fluorescence spectroscopy. VCF allows ion channel researchers to link dynamic structural changes, measured in real time, to function. Acid-sensing ion channels (ASICs) are Na+-permeable non-voltage-gated ion channels of the central and peripheral nervous system. They function as pH sensors, triggering neuronal excitation when pH decreases. Animal studies have shown the importance of ASICs for pain and fear sensation, learning, and neurodegeneration following ischaemic stroke. This review explores the technical bases and various developments of VCF, including fluorescence resonance energy transfer and the use of unnatural fluorescent amino acids. We provide an overview of VCF applications with a focus on ASICs, detailing how VCF has unveiled proton-induced conformational changes in key regions such as the acid pocket, wrist, and pore, crucial for understanding transitions between closed, open, and desensitized states.

E3 ubiquitin ligases regulate the composition of the proteome. These enzymes mono- or poly-ubiquitinate their substrates, directly altering protein function or targeting proteins for degradation by the proteasome. In this review, we discuss the opposing roles of human E3 ligases as effectors and targets in the evolutionary battle between host and pathogen, specifically in the context of SARS-CoV-2 infection. Through complex effects on transcription, translation, and protein trafficking, human E3 ligases can either attenuate SARS-CoV-2 infection or become vulnerabilities that are exploited by the virus to suppress the host's antiviral defenses. For example, the human E3 ligase RNF185 regulates the stability of SARS-CoV-2 envelope protein through the ubiquitin-proteasome pathway, and depletion of RNF185 significantly increases SARS-CoV-2 viral titer (iScience (2023) 26, 106601). We highlight recent advances that identify functions for numerous human E3 ligases in the SARS-CoV-2 life cycle and we assess their potential as novel antiviral agents.

Protein arginine methylation is a versatile post-translational protein modification that has notable cellular roles such as transcriptional activation or repression, cell signaling, cell cycle regulation, and DNA damage response. However, in spite of their extensive significance in the biological system, there is still a significant gap in understanding of the entire function of the protein arginine methyltransferases (PRMTs). It has been well-established that PRMTs form homo-oligomeric complexes to be catalytically active, but in recent years, several studies have showcased evidence that different members of PRMTs can have cross-talk with one another to form hetero-oligomeric complexes. Additionally, these heteromeric complexes have distinct roles separate from their homomeric counterparts. Here, we review and highlight the discovery of the heterodimerization of PRMTs and discuss the biological implications of these hetero-oligomeric interactions.

Mitochondria maintain organellar homeostasis through multiple quality control pathways, including the clearance of defective or unwanted mitochondria by selective autophagy. This removal of mitochondria, mitophagy, is controlled in large part by the outer mitochondrial membrane mitophagy receptors BNIP3 and NIX. While it has long been appreciated that BNIP3 and NIX mediate mitophagy by controlling the recruitment of autophagic machinery to the mitochondrial surface, the requirement for the carefully controlled spatiotemporal regulation of receptor-mediated mitophagy has only recently come to light. Several new factors that regulate the BNIP3/NIX-mediated mitophagy pathway have emerged, and various loss-of-function cell and animal models have revealed the dire consequences of their dysregulation. In this mini-review, we discuss new insights into the mechanisms and roles of the regulation of BNIP3 and NIX and highlight questions that have emerged from the identification of these new regulators.

Autism spectrum disorders (ASD) are a heterogenous set of syndromes characterised by social impairment and cognitive symptoms. Currently, there are limited treatment options available to help people with ASD manage their symptoms. Understanding the biological mechanisms that result in ASD diagnosis and symptomatology is an essential step in developing new interventional strategies. Human genetic studies have identified common gene variants of small effect and rare risk genes and copy number variants (CNVs) that substantially increase the risk of developing ASD. Reverse translational studies using rodent models based on these genetic variants provide new insight into the biological basis of ASD. Here we review recent findings from three ASD associated CNV mouse models (16p11.2, 2p16.3 and 22q11.2 deletion) that show behavioural and cognitive phenotypes relevant to ASD. These models have identified disturbed excitation-inhibition neurotransmitter balance, evidenced by dysfunctional glutamate and GABA signalling, as a key aetiological mechanism. These models also provide emerging evidence for serotoninergic neurotransmitter system dysfunction, although more work is needed to clarify the nature of this. At the brain network level, prefrontal cortex (PFC) dysfunctional connectivity is also evident across these models, supporting disturbed PFC function as a key nexus in ASD aetiology. Overall, published data highlight the utility and valuable insight gained into ASD aetiology from preclinical CNV mouse models. These have identified key aetiological mechanisms that represent putative novel therapeutic targets for the treatment of ASD symptoms, making them useful translational models for future drug discovery, development and validation.

Immunotherapy has emerged as a therapeutic option for many cancers. For some tumors, immune checkpoint inhibitors show great efficacy in promoting anti-tumor immunity. However, not all tumors respond to immunotherapies. These tumors often exhibit reduced inflammation and are resistant to checkpoint inhibitors. Therapies that turn these 'cold' tumors 'hot' could improve the efficacy and applicability of checkpoint inhibitors, and in some cases may be sufficient on their own to promote anti-tumor immunity. One strategy to accomplish this goal is to activate innate immunity pathways within the tumor. Here we describe how this can be accomplished by activating double-stranded RNA (dsRNA) sensors. These sensors evolved to detect and respond to dsRNAs arising from viral infection but can also be activated by endogenous dsRNAs. A set of proteins, referred to as suppressors of dsRNA sensing, are responsible for preventing sensing 'self' dsRNA and activating innate immunity pathways. The mechanism of action of these suppressors falls into three categories: (1) Suppressors that affect mature RNAs through editing, degradation, restructuring, or binding. (2) Suppressors that affect RNA processing. (3) Suppressors that affect RNA expression. In this review we highlight suppressors that function through each mechanism, provide examples of the effects of disrupting those suppressors in cancer cell lines and tumors, and discuss the therapeutic potential of targeting these proteins and pathways.