Biological Chemistry最新文献

Intersectins with their numerous protein interaction domains serve as versatile scaffolds for a range of membrane-associated processes. While being originally characterized as endocytic proteins, their functions clearly extend beyond the scaffolding of endocytic machinery. By interacting with and stabilizing important cellular signaling components, ranging from neurotransmitter receptors to complexes involved in neuronal guidance, intersectins play a key role in shaping neuronal processes. Consequently, intersectin deficiency in model organisms causes the most severe impairments in the brain, illustrating their crucial function for neuronal development and neurotransmission. In line with this, mutations in the human gene encoding intersectin 1 (ITSN1) have been linked to neurodevelopmental and neuropsychiatric disorders. In addition, haploinsufficiency of ITSN1 has recently been associated with an increased risk of Parkinson´s disease. In this review, we will discuss our current knowledge regarding the molecular functions of intersectins in order to better understand the pathological consequences of intersectin deficiency.

The endolysosomal system connects Golgi and plasma membrane to the degradative pathway towards the lysosome and therefore presents a crossroads for endocytic recycling, secretory transport and degradation. This complexity makes protein sorting and trafficking within the endolysosomal system challenging, and it requires tight regulation so that all proteins localize correctly. Proteins are sorted by distinct sorting adaptors, which recognize sorting signals and subsequently facilitate formation of transport carriers, which deliver content to other organelles. Alternatively, organelle maturation allows passive protein transport along different trafficking routes including endosomal and autophagosomal maturation. In this review, we will provide a bird's eye overview of the divers routes along which proteins are transported within the endolysosomal system and highlight open questions in the field.

In cardiomyocytes, the basic contractile unit are sarcomeres, which are organized in a regular manner facilitating their function. Here, we present a new computational approach to assess the functional properties of sarcomeres at the nanoscale level in human cardiac cells, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). We combined our analysis to different types of high-resolution imaging data, structured illumination microscopy (SIM), stimulated emission depletion (STED) microscopy-based imaging, as well as confocal microscopy data. We show that the radially averaged magnitude spectrum (RAMS) revealed sarcomere properties in a human cardiomyocyte model, iPSC-CMs, and compared our RAMS-based analysis to a real-space approach based on manually selected regions of interest. Moreover, we found the RAMS method suitable to quantify molecular differences of sarcomeres such as present in severe cardiac diseases, such as dilated cardiomyopathy (DCM). Defects in the sarcomere organization that occur in the presence of inherited DCM mutations in sarcomere proteins were efficiently recapitulated by our analysis. This new approach may facilitate streamlined analysis of molecular disease-specific phenotypic imaging data of cardiac cells, aiding our deeper understanding of the molecular basis of cardiac diseases.

Ras is a key regulator of signal transduction in cells. Ras malfunction is associated with a huge variety of oncological diseases. It is turned off by hydrolysis of bound GTP, which is accelerated by GTPase-activating proteins (GAPs). This minireview discusses the mechanism of Ras-catalyzed GTP hydrolysis, focusing on conformational dynamics and catalytic mechanisms. We discuss structural changes and the role of key residues such as Thr35, Gly60, Tyr32, Gln61, Gly12, and Gly13. Biophysical techniques such as X-ray crystallography, time-resolved FTIR spectroscopy, and hybrid quantum mechanics/molecular mechanics calculations have revealed the detailed reaction mechanisms, including the entry of the arginine finger and the rate-limiting step of inorganic phosphate release. Recent studies on the hydrolysis mechanism favor a solvent-assisted pathway. In addition, we summarize recent advances in Ras-targeting drugs.

Eukaryotic life is defined by the presence of organelles. Organelles, in turn, were classically defined as specialized membrane-bound compartments composed of a unique set of macromolecules which support specific functions. Over the last few decades, a concerted effort into uncovering which components are present in each organelle has shaped our view of cell biology. However, despite some organelles already being visualized over 100 years ago, we are still discovering new organelle residents. Furthermore, our concept of both 'organelles' and 'compartmentalization' has evolved together with our deepening understanding in a number of fields. These include: organelle substructure and organization; the network of contact sites which interconnects all organelles; and membraneless organelles and phase-separated condensates. This review explores how image- and mass spectrometry-based methods can be used to understand the spectrum of where components are localized: from complexes, to subdomains, and whole organelles. The components we mainly focus on are proteins of the mitochondria and secretory pathway organelles.

The literature on the lipid droplet organization (LDO) proteins Ldo16 and Ldo45 reads like a guided tour through the lipid droplet life cycle. Both yeast Ldo16/45 and their metazoan counterparts, the LDAF1/promethin proteins, were originally identified based on their connection to the lipodystrophy protein seipin, a key player in lipid droplet biogenesis. Mechanistic follow-up studies support a role of LDAF1/LDO as conserved integral component of the seipin lipid droplet biogenesis complex. However, at the same time, additional LDO functions beyond lipid droplet formation were identified in yeast. Together with Vac8, Ldo16/45 act as tethers for formation of vacuole lipid droplet (vCLIP) contact sites, structures that are crucial for lipid droplet breakdown via microautophagy during glucose starvation. Ldo45 additionally recruits the lipid transfer protein Pdr16 to vCLIP. Furthermore, Ldo16 was identified as a central player in the process of actomyosin-based lipid droplet motility, by acting as a receptor for the myosin adaptor protein Ldm1. Based on these findings, we suggest an overarching molecular role of the LDO proteins as multifunctional lipid droplet surface receptors that are optimized to coordinate the different aspects of the lipid droplet life cycle through an interplay with different effector proteins.

The diverse, and sometimes opposing, roles of mitochondria require sophisticated organizational and regulatory strategies. This review examines emerging evidence that mitochondria can solve this challenge through functional specialization - adopting distinct bioenergetic and metabolic programs based on location, contacts, and cellular conditions. We discuss both established principles and recent technological breakthroughs that reveal this hidden complexity. Ongoing advances promise to move the field from describing mitochondrial diversity to uncovering its regulatory mechanisms and therapeutic potential.

The phylum Euglenozoa, within the Eukaryote domain, includes diverse protists such as the medically significant kinetoplastids, characterized by their unique kinetoplast DNA. Both kinetoplastids and their sister class Diplonemea possess glycosomes - specialized microbodies that compartmentalize glycolysis and other metabolic pathways. Glycosomes likely evolved in a common ancestor of kinetoplastid and diplonemids, conferring metabolic flexibility and reducing cellular toxicity. These organelles are essential for parasite survival and thus, represent promising drug targets for treating kinetoplastid diseases. While the basic principles of peroxisome and glycosome biogenesis are conserved, distinct features in glycosome biogenesis machinery and a lower level of sequence conservation enables pathogen specific drug design for developing new therapies. This review summarizes our current knowledge on glycosome biogenesis, recent advances, and therapeutic potential for treating trypanosomatid infections.

Dendritic spines are the postsynaptic compartment of most excitatory synapses in the vertebrate brain. Their morphology is defined by a complex actin scaffold consisting of branched and unbranched actin filaments (F-actin), which constitute the major structural component of dendritic spines. During brain development, dendritic spines arise from dendritic filopodia, motile finger-like dendritic protrusions, whose morphology is also defined by an actin scaffold. The organization of the actin scaffold as well as its dynamic behavior in both dendritic filopodia and dendritic spines requires the coordinated activity of actin binding proteins (ABP) that promote either assembly or disassembly of F-actin. Studies of the past two decades identified a number of ABP and upstream regulatory pathways that control the morphology of dendritic spines as well as their morphological changes associated with synaptic plasticity, the cellular basis for learning and memory. Instead, much less is known about actin regulatory mechanisms that control the formation and elongation of dendritic filopodia or the structural changes associated with their transition into dendritic spines. This review article highlights recent advances in the field by summarizing and discussing studies of the past few years that provided exciting novel insights into the molecular machinery that governs dendritic filopodia initiation and their maturation into dendritic spines.