title: The DNAJA2 substrate release mechanism is essential for chaperone-mediated folding.
abstract: DNAJA1 (DJA1/Hdj2) and DNAJA2 (DJA2) are the major J domain partners of human Hsp70/Hsc70 chaperones. Although they have overall similarity with the well characterized type I co-chaperones from yeast and bacteria, they are biologically distinct, and their functional mechanisms are poorly characterized. We identified DJA2-specific activities in luciferase folding and repression of human ether-a-go-go-related gene (HERG) trafficking that depended on its expression levels in cells. Mutations in different internal domains of DJA2 abolished these effects. Using purified proteins, we addressed the mechanistic defects. A mutant lacking the region between the zinc finger motifs (DJA2-Δm2) was able to bind substrate similar to wild type but was incapable of releasing substrate during its transfer to Hsc70. The equivalent mutation in DJA1 also abolished its substrate release. A DJA2 mutant (DJA-221), which had its C-terminal dimerization region replaced by that of DJA1, was inactive but retained its ability to release substrate. The release mechanism required the J domain and ATP hydrolysis by Hsc70, although the nucleotide dependence diverged between DJA2 and DJA1. Limited proteolysis suggested further conformational differences between the two wild-type co-chaperones and the mutants. Our results demonstrate an essential role of specific DJA domains in the folding mechanism of Hsc70.
authors.affiliation: Department of Biochemistry, McGill University and Groupe de Recherche Axé sur la Structure des Protéines, Montreal, Quebec H3G 0B1, Canada.
authors.forename: Imad
authors.initials: I
authors.lastname: Baaklini
authors.forename: Michael J H
authors.initials: MJ
authors.lastname: Wong
authors.forename: Christine
authors.initials: C
authors.lastname: Hantouche
authors.forename: Yogita
authors.initials: Y
authors.lastname: Patel
authors.forename: Alvin
authors.initials: A
authors.lastname: Shrier
authors.forename: Jason C
authors.initials: JC
authors.lastname: Young
mesh_terms: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D017510:Protein Folding; D021381:Protein Transport / Q000502:physiology; D059748:Proteolysis; D016335:Zinc Fingers / Q000502:physiology
chemical_list: C107481:DNAJA1 protein, human; C494645:DNAJA2 protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; C494371:HSPA8 protein, human; C000606913:KCNH2 protein, human