Affiliation:
1. Daniel B. Warnell School of Forest Resources and Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602-2152
Abstract
ABSTRACT
A gene (
yacK
) encoding a putative multicopper oxidase (MCO) was cloned from
Escherichia coli
, and the expressed enzyme was demonstrated to exhibit phenoloxidase and ferroxidase activities. The purified protein contained six copper atoms per polypeptide chain and displayed optical and electron paramagnetic resonance (EPR) spectra consistent with the presence of type 1, type 2, and type 3 copper centers. The strong optical
A
610
(Ε
610
= 10,890 M
−1
cm
−1
) and copper stoichiometry were taken as evidence that, similar to ceruloplasmin, the enzyme likely contains multiple type 1 copper centers. The addition of copper led to immediate and reversible changes in the optical and EPR spectra of the protein, as well as decreased thermal stability of the enzyme. Copper addition also stimulated both the phenoloxidase and ferroxidase activities of the enzyme, but the other metals tested had no effect. In the presence of added copper, the enzyme displayed significant activity against two of the phenolate siderophores utilized by
E. coli
for iron uptake, 2,3-dihydroxybenzoate and enterobactin, as well as 3-hydroxyanthranilate, an iron siderophore utilized by
Saccharomyces cerevisiae
. Oxidation of enterobactin produced a colored precipitate suggestive of the polymerization reactions that characterize microbial melanization processes. As oxidation should render the phenolate siderophores incapable of binding iron,
yacK
MCO activity could influence levels of free iron in the periplasm in response to copper concentration. This mechanism may explain, in part, how
yacK
MCO moderates the sensitivity of
E. coli
to copper.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
133 articles.
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