ISSN:
1432-1327
Keywords:
Key words Resonance Raman spectroscopy
;
Azurin
;
Cupredoxins
;
Axial ligands
;
NMR spectroscopy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Assignment of the resonance Raman (RR) spectrum of Ni(II)-substituted azurin II from Alcaligenes xylosoxidans (NCIMB 11015) using Ni isotope substitution reveals an anomalously low Ni-S(Cys) stretching frequency of 349 cm–1, suggesting the presence of significant axial-ligand bonding interactions. The X-ray crystal structure of Ni(II)-substituted azurin from Pseudomonas aeruginosa shows that there are two potential axial ligands to the Ni ion: a peptide carbonyl O at a distance of 2.46 Å, together with a long-range interaction from a methionine sulfur (S′) at a distance of 3.30 Å. Comparison of the RR properties of Ni(II)-substituted azurin II with stellacyanin (which contains an axial carbonyl ligand, but no methionine) suggests that the interaction from the carbonyl oxygen ligand alone is not sufficient to account for the weak Ni azurin metal-thiolate bond. Instead, it appears that a Ni-methionine bonding interaction is also required to explain the low Ni-S(Cys) stretching frequency in Ni(II)-substituted azurin II. This hypothesis is supported by NMR studies which show a large paramagnetic shift for the protons of the methionine side-chain. Thus, it appears that Ni-substituted azurin II is best described as five-coordinate, and that significant Ni(II)-methionine bonding interactions can occur at a distance of 3.3 Å.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050233
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