Research article summary (published 18 Oct 2009):

Copper binding to beta-2-microglobulin and its pre-amyloid oligomers.

Full Abstract

Beta-2-microglobulin (beta2m) deposits as amyloid fibrils in the musculoskeletal system of patients undergoing long-term dialysis treatment as a result of kidney failure. Previous work has shown that Cu(II) binding causes beta2m to organize into nativelike dimers and tetramers that precede amyloid formation. Cu(II) is then released from higher-order oligomers before mature Cu(II)-free amyloid fibrils are formed. While some of the Cu(II)-induced structural changes that enable beta2m self-assembly are starting to be revealed, the details of how the Cu(II) 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-beta2m interactions. We find that monomeric beta2m binds Cu(II) via the N-terminal amine, the amide of Gln2, His31, and Asp59. In the dimer and tetramer, Asp59 is no longer bound to Cu(II), but the other residues still comprise a well-defined albeit weaker binding site that is better able to release Cu(II). Consistent with this is the observation that a fraction of the tetrameric species no longer binds Cu(II) at this weakened binding site, which agrees with a previous report that suggested the tetramer as the first Cu(II)-free oligomer. Our results also provide some insight into structural changes caused by Cu(II) binding that facilitate oligomer formation. Specifically, binding by Asp59 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 Cu(II) 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 Glu16. Overall, our measurements suggest that the previously proposed conformational switch caused by Cu(II) 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.

Author information

Author/s: Srikanth, Rapole (R); Mendoza, Vanessa Leah (VL); Bridgewater, Juma D (JD); Zhang, Guanshi (G); Vachet, Richard W (RW);

Affiliation: Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.

Grants: R01 GM 075092 (Agency:NIGMS NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural

Journal: Biochemistry (Biochemistry), published in United States. (Language: eng)

Reference: 2009-Oct; vol 48 (issue 41) : pp 9871-81

Dates: Created 2009/10/13; Completed 2009/11/02;

PMID: 19754160, status: MEDLINE (last retrieval date: 11/2/2009, IMS Date: )

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Binding Sites Chromatography, Liquid Copper - metabolism Dimerization Humans Isomerism Kidney Failure - metabolism Kinetics

Kinetics Mass Spectrometry Models, Molecular Musculoskeletal Diseases - metabolism Oxidation-Reduction Protein Conformation Static Electricity beta 2-Microglobulin - chemistry; metabolism

Associated Chemicals: beta 2-Microglobulin (0) ; Copper (7440-50-8)

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