NMR Solution Structure of the Oxidized Form of MerP, a Mercuric Ion Binding Protein Involved in Bacterial Mercuric Ion Resistance

Mercuric ions are toxic to living organisms because of their strong affinity for cysteine residues in proteins. Some bacteria have developed a resistance mechanism whereby Hg2+ is transported into the cytoplasm and reduced to Hg0. One of the proteins involved in the transport of mercuric ion is the...

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Bibliographic Details
Published in:Biochemistry (Easton) 1998-06, Vol.37 (26), p.9316-9322
Main Authors: Qian, Hong, Sahlman, Lena, Eriksson, Per-Olof, Hambraeus, Charlotta, Edlund, Ulf, Sethson, Ingmar
Format: Article
Language:English
Subjects:
Bacterial Proteins - chemistry
Bacterial Proteins - physiology
Carrier Proteins - chemistry
Carrier Proteins - physiology
Crystallography, X-Ray
Drug Resistance, Microbial
Escherichia coli - chemistry
Escherichia coli - drug effects
Hydrogen-Ion Concentration
Mercury - metabolism
Mercury - pharmacology
Models, Molecular
Nuclear Magnetic Resonance, Biomolecular
Oxidation-Reduction
Oxidoreductases - metabolism
Protein Binding
Protein Structure, Secondary
Proteins
Solutions
Surface Properties
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Summary:Mercuric ions are toxic to living organisms because of their strong affinity for cysteine residues in proteins. Some bacteria have developed a resistance mechanism whereby Hg2+ is transported into the cytoplasm and reduced to Hg0. One of the proteins involved in the transport of mercuric ion is the periplasmic binding protein MerP, which can exist both as oxidized (disulfide) and as reduced (dithiol) forms. Only the reduced form with Cys-17 and Cys-14 residues as free thiols is a potent receptor for mercuric ion. In this work the solution structure of the oxidized form of MerP has been determined by multidimensional NMR spectroscopy and compared to the NMR structures of the previously published structures of the reduced and mercury-bound forms of MerP. The mercury-bound and oxidized forms have similar tertiary structures, whereas in the reduced form there is a large rearrangement of the mercuric ion binding loop and the nearby loop comprising residues 38−41. The structural arrangement of the latter loop seems to be important for the stabilization of the surface location of the cysteine-containing loop. In the reduced form at low pH the cysteine-containing loop adopts a conformation similar to what is observed in the oxidized and mercury-bound forms. The oxidized form also differs with respect to the other two forms in the relative positions of some of the α-helices and β-strands. Structural differences between the oxidized and reduced forms may help explain why the reduced form is stable in the periplasm, which is considered to be an oxidizing environment.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi9803628