Understanding the Function and Regulation of the DNAJB2 Chaperone

DNAJB2 is a co-chaperone of the Hsp70 system and is highly expressed in the nervous system, especially in neurons. Like other family members of the class B J-domain protein (JDP) family, DNAJB2 contains a conserved J-domain, which can activate Hsp70, and a GF-rich region that folds onto the J-domain, regulating Hsp70 binding. However, no structural information is currently available for DNAJB2, and we therefore lack a mechanistic understanding of its function and regulation.

Here, we have studied the structure and function of DNAJB2 by combining NMR spectroscopy with biophysical and biochemical methodologies. We show that DNAJB2 chaperone assembles into octameric complexes that show potent aggregation-prevention activity towards amorphous aggregates. In addition, we have solved an NMR structure of DNAJB2 C-terminal region, which contains a C-terminal substrate binding domain (CTD), and a ubiquitin binding motif (UIM). The presence of two tandem UIMs is unique to DNAJB2 among the J-domain proteins, and suggests that this chaperone may possibly form a link between the cellular protein folding and degradation machineries. Through NMR measurements, we have mapped the binding sites on these domains for both aggregated substrate proteins and mono-ubiquitin.

Furthermore, we have showed that while the inhibition mechanism for the regulation of Hsp70 binding to DNAJB2 is conserved among class B JDPs, the mechanism of its release in DNAJB2 is different than in its canonical homologs. We are currently exploring alternative release mechanisms and their consequences on the chaperone’s functions.