DNAJB8 oligomerization is mediated by an aromatic-rich motif that is dispensable for substrate activity

Abstract

SUMMARYJ-domain protein (JDP) molecular chaperones have emerged as central players that maintain a healthy proteome. The diverse members of the JDP family function as monomers/dimers and a small subset assemble into micron-sized oligomers. The oligomeric JDP members have eluded structural characterization due to their low-complexity, intrinsically disordered middle domains. This in turn, obscures the biological significance of these larger oligomers in protein folding processes. Here, we identified a short, aromatic motif within DNAJB8, that drives self-assembly through π-π stacking and determined its X-ray structure. We show that mutations in the motif disrupt DNAJB8 oligomerizationin vitroand in cells. DNAJB8 variants that are unable to assemble bind to misfolded tau seeds more specifically and retain capacity to reduce protein aggregationin vitroand in cells. We propose a new model for DNAJB8 function in which the sequences in the low-complexity domains play distinct roles in assembly and substrate activity.

Tertiary structure and conformational dynamics of the anti-amyloidogenic chaperone DNAJB6b at atomistic resolution

“…The equivalent peptide in DNAJB6b can be hypothesized to be 153 GFSSFD 158 , which indeed is mostly exposed when DNAJB6b is in its extended state. It was found that for DNAJB8, mutations in this peptide did abolish self-oligomerization and lead to DNAJB8 monomerization; this monomeric DNAJB8, however, did retain wildtype activity in terms of substrate binding and chaperone function [53]. This would imply that substrate-binding and self-oligomerization are driven by the same S/T domain, and that monomers are the functional chaperone moieties, and self-oligomerization may only happen at high concentrations in the absence of clients.…”

“…Another still open question relates to the role of self-oligomerization of the DNAJB6-subgroup. A recent study on DNAJB8 revealed that this is related to a specific peptide ( 147 AFSSFN 152 ) within the S/T rich region [53]. The equivalent peptide in DNAJB6b can be hypothesized to be 153 GFSSFD 158 , which indeed is mostly exposed when DNAJB6b is in its extended state.…”

Factors Affecting Protein Recovery During Hsp40 Affinity Profiling

“…One interesting unaddressed question is the role of DNJAB8 oligomerization. DNAJB8 and the structurally similar DNAJB6 form a distribution of oligomeric, dimeric, and monomeric stables, while DNAJB1 forms dimers [26,42,43].…”