Copper binding to XXXX and its pre-amyloid oligomers.

@entity1 @entity8863 @entity2262 @entity6115 @entity177 @entity367 @entity6346 @entity2574
@entity2262 ( @entity2262 ) deposits as amyloid fibrils in the musculoskeletal system of @entity1 undergoing long-term dialysis treatment as a result of @entity177 . Previous work has shown that @entity8863 binding causes @entity2262 to organize into nativelike dimers and tetramers that precede amyloid formation. @entity8863 is then released from higher-order oligomers before mature @entity8863 -free amyloid fibrils are formed. While some of the @entity8863 -induced structural changes that enable @entity2262 self-assembly are starting to be revealed, the details of how the @entity8863 binding site evolves from the monomer to the dimers and tetramers are not known. Here, we report results from three mass spectrometry (MS)-based methods that provide insight into the changing Cu- @entity2262 interactions. We find that monomeric @entity2262 binds @entity8863 via the N-terminal @entity6115 , the @entity6346 of Gln2, His31, and @entity2574 59. In the dimer and tetramer, @entity2574 59 is no longer bound to @entity8863 , but the other residues still comprise a well-defined albeit weaker binding site that is better able to release @entity8863 . Consistent with this is the observation that a fraction of the tetrameric species no longer binds @entity8863 at this weakened binding site, which agrees with a previous report that suggested the tetramer as the first @entity8863 -free oligomer. Our results also provide some insight into structural changes caused by @entity8863 binding that facilitate oligomer formation. Specifically, binding by @entity2574 59 in the monomer requires significant movement of this residue, and we propose that this repositioning is important for establishing a pair of dimer-stabilizing salt bridges between this residue and Lys19. We also find evidence that @entity8863 binding in the N-terminal region of the monomer repels Arg3, which likely allows this residue to form a pair of dimer-stabilizing salt bridges with @entity367 16. Overall, our measurements suggest that the previously proposed conformational switch caused by @entity8863 binding includes not only a cis-trans isomerization at Pro32 but also the repositioning of residues that are critical for the formation of new electrostatic interactions.
