Project description:The E3 ubiquitin ligases CHIP/CHN-1 and UFD-2 team up to accelerate ubiquitin chain formation. However, it remained largely unclear how the high processivity of this E3 set is achieved. Here we studied the molecular mechanism and function of the CHN-1/UFD-2 complex in Caenorhabditis elegans. Our data show that UFD-2 binding promotes the cooperation between CHN-1 and ubiquitin-conjugating E2 enzymes by stabilizing CHN-1 U-box dimer. The HSP-1 chaperone outcompetes UFD-2 for CHN-1 binding and promotes the auto-inhibited CHN-1 state by acting on the conserved position of the U-box domain. The interaction with UFD-2 enables CHN-1 to efficiently ubiquitinate S-Adenosylhomocysteinase (AHCY-1), an enzyme crucial for lipid metabolism. Our results define the molecular mechanism underlying the synergistic cooperation of CHN-1 and UFD-2 in substrate ubiquitylation.
Project description:Enterovirus 71 (EV71) belongs to human enterovirus species A of the genus Enterovirus within the family Picornaviridae. We established transformant cells by transfection of mouse cells with genomic DNA from human cells and then detected two EV71-susceptible cell lines. Using microarray with the two cell lines we found that scavenger receptor B2 is a cellular receptor for EV71.
Project description:Proteostasis is achieved by quality control pathways that support the generation of correctly folded proteins, prevent protein misfolding and remove toxic proteins. The quality control E3 ligase CHIP ubiquitylates damaged proteins consigned by chaperone partners for disposal through the endo-lysosomal pathway, proteasomal degradation, or autophagy. Additionally, CHIP has been reported to modulate essential signaling pathways by precisely delivering a myriad of native proteins to destined fates. We aimed at understanding the substrate specificity and processivity through a “structure to function” approach, by examining the modeled 3D structure of the C. elegans ortholog of CHIP, CHN-1, based on the reported structure of murine CHIP. Using different model organisms and various genetic and biochemical analyses, we demonstrate that monomeric CHN-1/CHIP has preserved ubiquitylation activity and promotes longevity via the IIS pathway. The lack of monomer results in premature aging and neurodegenerative disorder. Our data reveal that autoubiquitylation plays an important role in the alteration between monomer and dimer. Together, the conserved dimer-monomer transition provides a molecular switch regulating CHIP activity in response to proteotoxic stress and aging.