Allosteric regulation of the 20S proteasome by the Catalytic Core Regulators (CCRs) family.

Controlled degradation of proteins is necessary for ensuring their abundance and sustaining a healthy and accurately functioning proteome. One of the degradation routes involves the uncapped 20S proteasome, which cleaves proteins with a partially unfolded region, including those that are damaged or contain intrinsically disordered regions. This degradation route is tightly controlled by a recently discovered family of proteins named Catalytic Core Regulators (CCRs).

Regulation of the 20S Proteasome by a Novel Family of Inhibitory Proteins.

The protein degradation machinery plays a critical role in the maintenance of cellular homeostasis, preventing the accumulation of damaged or misfolded proteins and controlling the levels of regulatory proteins. The 20S proteasome degradation machinery, which predominates during oxidative stress, is able to cleave any protein with a partially unfolded region, however, uncontrolled degradation of the myriad of potential substrates is improbable. This study aimed to identify and characterize the regulatory mechanism that controls 20S proteasome-mediated degradation.

The Contribution of the 20S Proteasome to Proteostasis.

The last decade has seen accumulating evidence of various proteins being degraded by the core 20S proteasome, without its regulatory particle(s). Here, we will describe recent advances in our knowledge of the functional aspects of the 20S proteasome, exploring several different systems and processes. These include neuronal communication, post-translational processing, oxidative stress, intrinsically disordered protein regulation, and extracellular proteasomes.

The first Autumn School on Proteostasis: from molecular mechanisms to organismal consequences.

The first Autumn School on Proteostasis was held at the Mediterranean Institute for Life Sciences (MedILS) in Split, Croatia, from November 12th-16th, 2018, bringing together 44 graduate students and postdoctoral fellows and 22 principal investigators from around the world. This meeting was geared towards providing students with an in-depth understanding of the field of proteostasis, with the aim of broadening their perspectives of the field. Session topics covered multiple aspects of cellular and organismal proteostasis, including fundamental principles, responses to heat shock, aging and disease, and protein folding, misfolding, and degradation.

Mass Spectrometry: A Technique of Many Faces.

Protein complexes form the critical foundation for a wide range of biological process, however understanding the intricate details of their activities is often challenging. In this review we describe how mass spectrometry plays a key role in the analysis of protein assemblies and the cellular pathways which they are involved in. Specifically, we discuss how the versatility of mass spectrometric approaches provides unprecedented information on multiple levels.

Plasmodium actin is incompletely folded by heterologous protein-folding machinery and likely requires the native Plasmodium chaperonin complex to enter a mature functional state.

Actin filament turnover underpins several processes in the life cycle of the malaria parasite, Plasmodium falciparum. Polymerization and depolymerization are especially important for gliding motility, a substrate-dependent form of cell movement that underpins the protozoan parasite's ability to disseminate and invade host cells. To date, given difficulties in extraction of native actins directly from parasites, much of our biochemical understanding of malarial actin has instead relied on recombinant protein extracted and purified from heterologous protein expression systems.

Plasmodium falciparum coronin organizes arrays of parallel actin filaments potentially guiding directional motility in invasive malaria parasites.

Background: Gliding motility in Plasmodium parasites, the aetiological agents of malaria disease, is mediated by an actomyosin motor anchored in the outer pellicle of the motile cell. Effective motility is dependent on a parasite myosin motor and turnover of dynamic parasite actin filaments. To date, however, the basis for directional motility is not known.

Disassembly activity of actin-depolymerizing factor (ADF) is associated with distinct cellular processes in apicomplexan parasites.

Proteins of the actin-depolymerizing factor (ADF)/cofilin family have been shown to be crucial for the motility and survival of apicomplexan parasites. However, the mechanisms by which ADF proteins fulfill their function remain poorly understood. In this study, we investigate the comparative activities of ADF proteins from Toxoplasma gondii and Plasmodium falciparum, the human malaria parasite, using a conditional T.

A mechanism for actin filament severing by malaria parasite actin depolymerizing factor 1 via a low affinity binding interface.

Actin depolymerizing factor (ADF)/cofilins are essential regulators of actin turnover in eukaryotic cells. These multifunctional proteins facilitate both stabilization and severing of filamentous (F)-actin in a concentration-dependent manner. At high concentrations ADF/cofilins bind stably to F-actin longitudinally between two adjacent actin protomers forming what is called a decorative interaction.

The dendritic cell receptor Clec9A binds damaged cells via exposed actin filaments.

The immune system must distinguish viable cells from cells damaged by physical and infective processes. The damaged cell-recognition molecule Clec9A is expressed on the surface of the mouse and human dendritic cell subsets specialized for the uptake and processing of material from dead cells. Clec9A recognizes a conserved component within nucleated and nonnucleated cells, exposed when cell membranes are damaged.

Holding back the microfilament--structural insights into actin and the actin-monomer-binding proteins of apicomplexan parasites.

Parasites from the phylum Apicomplexa are responsible for several major diseases of man, including malaria and toxoplasmosis. These highly motile protozoa use a conserved actomyosin-based mode of movement to power tissue traversal and host cell invasion. The mode termed as 'gliding motility' relies on the dynamic turnover of actin, whose polymerisation state is controlled by a markedly limited number of identifiable regulators when compared with other eukaryotic cells.

Spatial localisation of actin filaments across developmental stages of the malaria parasite.

Actin dynamics have been implicated in a variety of developmental processes during the malaria parasite lifecycle. Parasite motility, in particular, is thought to critically depend on an actomyosin motor located in the outer pellicle of the parasite cell. Efforts to understand the diverse roles actin plays have, however, been hampered by an inability to detect microfilaments under native conditions.

Killer cell immunoglobulin-like receptor 3DL1-mediated recognition of human leukocyte antigen B.

Members of the killer cell immunoglobulin-like receptor (KIR) family, a large group of polymorphic receptors expressed on natural killer (NK) cells, recognize particular peptide-laden human leukocyte antigen (pHLA) class I molecules and have a pivotal role in innate immune responses. Allelic variation and extensive polymorphism within the three-domain KIR family (KIR3D, domains D0-D1-D2) affects pHLA binding specificity and is linked to the control of viral replication and the treatment outcome of certain haematological malignancies. Here we describe the structure of a human KIR3DL1 receptor bound to HLA-B*5701 complexed with a self-peptide.

Tracking mutant huntingtin aggregation kinetics in cells reveals three major populations that include an invariant oligomer pool.

Huntington disease is caused by expanded polyglutamine sequences in huntingtin, which procures its aggregation into intracellular inclusion bodies (IBs). Aggregate intermediates, such as soluble oligomers, are predicted to be toxic to cells, yet because of a lack of quantitative methods, the kinetics of aggregation in cells remains poorly understood. We used sedimentation velocity analysis to define and compare the heterogeneity and flux of purified huntingtin with huntingtin expressed in mammalian cells under non-denaturing conditions.