Background: Self-association of the HRD complex is important for its function in ER quality control, but the oligomeric state of the complex is still unclear. Results: The luminal component Yos9 dimerizes independently. Conclusion: Dimerization of Yos9 suggests a dimeric state of the HRD complex. Significance: The assembly of a functional HRD complex oligomer is further elucidated on a structural level.
Large ring ATPases that organize mitotic chromosomes. Christian Haering, EMBL, HeidelbergTwo multi-subunit protein complexes named cohesin and condensin are key components of the cell's mitotic and meiotic chromosome segregation machineries. Cohesin physically links the replicated sister chromatids and thereby allows their bi-polar orientation on the mitotic spindle. Once all sister chromatids have been successfully bi-oriented, cleavage of one of cohesin's subunits by the site-specific protease separase releases their linkage and triggers chromosome movement to the poles. Condensin is essential for holding chromosomes in a compact shape during their movements and thereby prevents them from getting entangled or trapped in the middle of the dividing cell. Both complexes are built upon two specific proteins of the Structural Maintenance of Chromosomes (SMC) family that bind to each other via hetero-dimerization domains at one end of 40-50nm long coiled-coils. The ABC ATPase head domains situated at the other ends of the coiled coils are connected by a third protein that is a member of the so-called kleisin protein family and recruits additional HEAT-repeat containing subunits to the complex. I will present evidence that cohesin and condensin bind chromosomes using a unique mechanism, namely by topologically entrapping them inside the large tripartite ring structure formed by their SMC and kleisin proteins, and discuss how cycles of ATP binding and hydrolysis by the SMC head domains may drive the conformational changes required for the organization of mitotic chromosomes.Transport of cargo between organelles in eukaryotic cells is mediated by vesicles that bud from a donor compartment and specifically fuse with an acceptor membrane. Currently, it is becoming clear that the underlying molecular machineries involved in the principal aspects of vesicular trafficking are highly conserved, not only between different species but also between different vesicle trafficking steps. In all steps, the central machinery involved in the fusion process is composed of members of the SNARE protein family. Distinctive, heterologous sets of SNARE proteins anchored in the vesicle and target membrane are thought to assemble in a zipper-like fashion into a four-helix bundle, providing the energy to mediate fusion of the two bilayers. Although SNAREs are sufficient to drive membrane fusion when inserted into liposome membranes, this minimal machinery is organized and controlled by additional factors in vivo. Members of the cytosolic Sec1/Munc18 (SM) family of proteins have been established as essential factors in different intracellular transport steps, during which they functionally interact with the SNARE machinery. To come to a better understanding of the molecular events during vesicle fusion, we focus on a detailed structural, kinetic, thermodynamic, and phylogenetic characterization of the core vesicle fusion machinery.To avoid accumulation of misfolded proteins in the endoplasmic reticulum, unfolded and misfolded proteins are dispo...
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