Biochemical Society transactions最新文献

The 70-kDa heat shock protein, Hsp70, is a key chaperone involved in cellular protein homeostasis. The structure of the Hsp70 protein family is highly conserved, including a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD). ATP binding and hydrolysis in the NBD of Hsp70 regulates the binding and release of substrates in the SBD via interdomain allosteric communication. Growing evidence shows that the conformational dynamics of Hsp70 are crucial for its function, which are difficult to probe by traditional bulk-based methods. Single-molecule techniques are emerging as powerful tools to explore the dynamics of proteins that are obscured in bulk measurements. In this review, we summarize recent progress in the study of the molecular dynamics of Hsp70 and its interactions with cochaperones and substrates using single-molecule fluorescence spectroscopy and single-molecule force spectroscopy. We discuss how the application of single-molecule techniques facilitates a deeper understanding of the mechanistic details of the chaperone functions of Hsp70.

Ankyrins are a family of intracellular scaffolding proteins that control the subcellular localization of a host of critically important signaling proteins within neurons, including many proteins associated with neurological disease. Ankyrin proteins are a vital component of the neuron. These scaffolding proteins must be spatially and temporally arranged to interact with their binding partners and facilitate proper neuronal signaling. Dysfunction of ankyrins is associated with neurodevelopmental disorders such as epilepsy and autism spectrum disorder. Despite the high degree of sequence similarity between ankyrin proteins, they display almost completely nonoverlapping localization and function. How ankyrins localize to the correct subcellular compartments to interact with their binding partners and complete their distinct roles remains poorly understood. Emerging evidence suggests that post-translational modifications may play a key part in this process. Some of the post-translational modifications that have been identified to regulate ankyrins are phosphorylation, ubiquitination, and palmitoylation. These modifications affect proper interactions, function, and localization of ankyrin proteins, which highlights their potential role in disease. This review will give an overview of neuronal ankyrins, and how post-translational modifications could be utilized to regulate protein localization and function in the context of neurological disease.

The endosomal system is essential for the intra- and intercellular communication in cells and multicellular organisms. It is involved in the secretion of signaling factors and serves as a venue for signaling receptors from the plasma membrane, which are endocytosed after ligand binding. Many internalized receptor-ligand complexes and numerous other endocytosed proteins arrive at the Rab5-positive early endosome, where they will be sorted. Cargoes marked with ubiquitin are bound by endosomal sorting complex required for transport (ESCRT)-0 and ESCRT-I complexes to initiate their degradation. The remaining cargoes are recycled back to the plasma membrane or the trans-Golgi network. To degrade ubiquitinated cargoes, the early endosome has to mature into a late endosomal structure, the multivesicular body (MVB). This procedure requires the Rab5-to-Rab7 conversion, mediated by the RABEX5-MON1/CCZ1 RabGEF cascade. Moreover, cargoes destined for degradation have to be packaged into intraluminal vesicles (ILVs) through ESCRT-III and Vps4. The matured late endosome or MVB finally fuses with a lysosome to degrade the cargo. Although ESCRT-mediated ILV formation and Rab conversion are well-characterized processes during endosome maturation, it remained until recently unclear whether these processes are connected. Lately, several studies were published illuminating the relationship of ESCRT functions and Rab conversion. Here, we review the current knowledge on the role of the ESCRT machinery in cargo degradation and RABEX5 regulation and MON1/CCZ1-mediated Rab conversion during endosome maturation. Moreover, we propose a model on the regulatory role of ESCRT functions during endosome maturation.

Protein lipidation is a collection of important post-translational modifications that modulate protein localization and stability. Protein lipidation affects protein function by facilitating interactions with cellular membranes, changing the local environment of protein interactions. Among these modifications, S-acylation has emerged as a key regulator of various cellular processes, including different forms of cell death. In this mini-review, we highlight the role of S-acylation in apoptosis and its emerging contributions to necroptosis and pyroptosis. While traditionally associated with the incorporation of palmitic acid (palmitoylation), recent findings indicate that other fatty acids can also participate in S-acylation, expanding its functional repertoire. In apoptosis, S-acylation influences the localization and function of key regulators such as Bcl-2-associated X protein and other proteins modulating their role in mitochondrial permeabilization and death receptor signaling. Similarly, in necroptosis, S-acylation of mixed lineage kinase domain-like protein (MLKL) with palmitic acid and very long-chain fatty acids enhances membrane binding and membrane permeabilization, contributing to cell death and inflammatory responses. Recent studies also highlight the role of S-acylation in pyroptosis, where S-acylated gasdermin D facilitates membrane localization and pore assembly upon inflammasome activation. Blocking palmitoylation has shown to suppress pyroptosis and cytokine release, reducing inflammatory activity and tissue damage in septic models. Collectively, these findings underscore S-acylation as a shared and important regulatory mechanism across cell death pathways affecting membrane association of key signaling proteins and membrane dynamics, and offer insights into the spatial and temporal control of protein function.

Many eukaryotic organisms, from ciliates to mammals, employ programmed DNA elimination during their postmeiotic reproduction. The process removes specific regions from the somatic DNA and has broad functions, including the irreversible silencing of genes, sex determination, and genome protection from transposable elements or integrating viruses. Multiple mechanisms have evolved that explain the sequence selectivity of the process. In some cases, the eliminated sequences lack centromeres and are flanked by conserved sequence motifs that are specifically recognized and cleaved by designated nucleases. Upon cleavage, all DNA fragments that lack centromeres are lost during the following mitosis. Alternatively, specific sequences can be destined for elimination by complementary small RNAs (sRNAs) as in some ciliates. These sRNAs enable a PIWI-mediated recruitment of chromatin remodelers, followed up by the precise positioning of a cleavage complex formed from a transposase like PiggyBac or Tc1. Here, we review the known molecular interplay of the cellular machinery that is involved in precise sRNA-guided DNA excision, and additionally, we highlight prominent knowledge gaps. We focus on the modes through which sRNAs enable the precise localization of the cleavage complex, and how the nuclease activity is controlled to prevent off-target cleavage. A mechanistic understanding of this process could enable the development of novel eukaryotic genome editing tools.

Almost all eukaryotic cells have the capacity to form lipid droplets (LDs) in conditions of excess energy. Traditionally thought to be just inert fat reservoirs, LDs have recently emerged as important metabolic regulators of cellular stress response that buffer excess free fats and protect cells from lipotoxicity. Ceramide is a bioactive lipid that accumulates in metabolic tissues during fat oversupply. Emerging evidence suggests that sphingolipids and sphingolipid-metabolizing enzymes are found in the LDs and affect LD biogenesis and functions. This article aims to summarize the evidence, delineate some plausible functions of ceramide in hepatic LD biogenesis, and illustrate some of the challenges in this novel field of research. We focus on the biogenesis of LDs in hepatocytes, the parenchymal cells of the liver, because non-alcoholic fatty liver disease is the quintessential manifestation of metabolic stress caused by fat oversupply.

Many bacteria divide by binary fission, producing two identical daughter cells, which requires proper placement of the division machinery at mid-cell. Spherical bacteria (cocci) face unique challenges due to their lack of natural polarity. In this review, we compile current knowledge on how cocci regulate cell division, how they select the proper division plane, and ensure accurate Z-ring positioning at mid-cell. While Streptococcus pneumoniae and Staphylococcus aureus are the most well-studied models for cell division in cocci, we also cover other less-characterized cocci across different bacterial groups and discuss the conservation of known Z-ring positioning mechanisms in these understudied bacteria.

Inducible protein degradation systems are an important but untapped resource for the study of protein function in plant cells. Unlike mutagenesis or transcriptional control, regulated degradation of proteins of interest allows the study of the biological mechanisms of highly dynamic cellular processes involving essential proteins. While systems for targeted protein degradation are available for research and therapeutics in animals, there are currently limited options in plant biology. Targeted protein degradation systems rely on target ubiquitination by E3 ubiquitin ligases. Systems that are available or being developed in plants can be distinguished primarily by the type of E3 ubiquitin ligase involved, including those that utilize Cullin-RING ligases, bacterial novel E3 ligases, and N-end rule pathway E3 ligases, or they can be controlled by proteolysis targeting chimeras. Target protein ubiquitination leads to degradation by the proteasome or targeting to the vacuole, with both pathways being ubiquitous and important for the endogenous control of protein abundance in plants. Targeted proteolysis approaches for plants will likely be an important tool for basic research and to yield novel traits for crop biotechnology.

Ubiquitination plays a key role in the regulation of numerous diverse cellular functions. This process involves the covalent attachment of ubiquitin to protein substrates by a cascade of enzymes. In recent years, various non-proteinaceous substrates of ubiquitination have been discovered, expanding the potential for the functions of ubiquitination beyond its conventional role as a post-translational modification. Here, we profile the non-proteinaceous substrates of ubiquitination reported to date, the enzymes that regulate these activities, and the mechanistic details of substrate modification. The biological functions linked to these modifications are discussed, and finally, we highlight the challenges hindering further progress in the identification and functional characterization of non-proteinaceous substrates of ubiquitination within cellular contexts.