期刊
BIOCHEMICAL JOURNAL
卷 413, 期 -, 页码 459-465出版社
PORTLAND PRESS LTD
DOI: 10.1042/BJ20080467
关键词
Bacillus subtilis; copper trafficking; copper-mediated dimerization; cysteine thiol; beta(2) formation constant
资金
- Biotechnology and Biological Sciences Research Council Funding Source: Medline
- Wellcome Trust Funding Source: Medline
CopZ, an Atx I-like copper chaperone from the bacterium Bacillus subtilis, functions as part of a complex cellular machinery for Cu(I) trafficking and detoxification, in which it interacts specifically with the transmembrane Cu(I)-transporter CopA. Here we demonstrate that the cysteine residues of the MXCXXC Cu(I)binding motif of CopZ have low proton affinities, with both exhibiting pK(a) values of 6 or below. Chelator competition experiments demonstrated that the protein binds Cu(1) with extremely high affinity, with a small but significant pH-dependence over the range pH 6.5-8.0. From these data, a pH-corrected formation constant, beta(2), = similar to 6 x 10(22) M-2, was determined. Rapid exchange of Cu(I) between CopZ and the Cu(I)-chelator BCS (bathocuproine disulfonate) indicated that the mechanism of exchange does not involve simple dissociation of Cu(I) from CopZ (or BCS), but instead proceeds via the formation of a transient Cu(I)-mediated protein-chelator complex. Such a mechanism has similarities to the Cu(I)exchange pathway that occurs between components of copper-trafficking pathways.
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