Amyloid-β oligomers are captured by the DNAJB6 chaperone: Direct detection of interactions that can prevent primary nucleation

Abstract

<jats:title>Abstract</jats:title><jats:p>A human molecular chaperone protein, DNAJB6, is an efficient inhibitor of amyloid aggregation owing to a unique motif with conserved S/T-residues with high capacity for hydrogen bonding. Global analysis of kinetics data previously showed that especially the primary nucleation rate is inhibited. It was concluded that DNAJB6 achieves this remarkably effective and sub-stoichiometric inhibition by interacting not with the monomeric unfolded conformations of the amyloid-β (Aβ) peptide but with aggregated species. The pre-nucleation oligomeric aggregates are transient and difficult to study experimentally. Here we employed an approach to directly detect oligomeric forms of Aβ formed in solution by subsequent analysis with native mass spectrometry (native MS). Results show that the signals from the various forms of Aβ (1-40) oligomers were reduced considerably in the presence of DNAJB6, but not with a mutational variant of DNAJB6 in which the S/T-residues were substituted. With focus on DNAJB6 we could also detect signals that appear to represent DNAJB6 dimers and trimers to which varying amounts of Aβ is bound. These data provide direct experimental evidence that it is the oligomeric forms of Aβ that are captured by DNAJB6 in a manner which is dependent on the S/T residues. Strong binding of Aβ oligomers to DNAJB6 should indeed inhibit the formation of amyloid nuclei, in agreement with the previously observed decrease in primary nucleation rate.</jats:p>

An S/T motif controls reversible oligomerization of the Hsp40 chaperone DNAJB6b through subtle reorganization of a β sheet backbone

“…Indeed, mutation of the ST16/ST17 sites to alanine, while retaining the oligomeric form of the protein, has a dramatic effect on the ability of DNAJB6b to inhibit amyloid β aggregation (16). This is presumably due to strand B1 being locked in a canonical straight conformation, effectively blocking subunit exchange between various oligomeric states of DNAJB6b that is paramount for inhibition of aggregation (43). Even a single-point mutation (T142A) in that region impacts the association and dissociation rates from the oligomeric species (Fig.…”

The unhappy chaperone

“…Crucially, experimental studies have failed to detect any direct interaction between DNAJB6 and Aβ42 monomers (Månsson et al, 2014b;Månsson et al, 2018), and an absence of strong interactions between the chaperone and amyloid peptide monomers in solution, which appears to be a recurring feature (Dedmon et al, 2005;Chien et al, 2010;Österlund et al, 2020). DNAJB6 inhibits nucleation of Aβ42 fibril formation, which has been interpreted in terms of interactions between the chaperone and oligomeric forms of the Aβ42 peptide (Månsson et al, 2014b;Österlund et al, 2020). Such a mechanism can explain the increased energy barrier for nucleation but not the shift of the final equilibrium state; as such, the elevated concentrations of peptide monomer at the end of the reaction in the presence of chaperone remains to be explained.…”