1bu5
From Proteopedia
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X-RAY CRYSTAL STRUCTURE OF THE DESULFOVIBRIO VULGARIS (HILDENBOROUGH) APOFLAVODOXIN-RIBOFLAVIN COMPLEX
Overview
The apoprotein of flavodoxin from Desulfovibrio vulgaris forms a complex, with riboflavin. The ability to bind riboflavin distinguishes this, flavodoxin from other short-chain flavodoxins which require the phosphate, of FMN for flavin binding. The redox potential of the, semiquinone/hydroquinone couple of the bound riboflavin is 180 mV less, negative than the corresponding complex with FMN. To elucidate the binding, of riboflavin, the complex has been crystallized and the crystal structure, solved by molecular replacement using native flavodoxin as a search model, to a resolution of 0.183 nm. Compared to the FMN complex, the, hydrogen-bonding network at the isoalloxazine sub-site of the riboflavin, complex is severely disrupted by movement of the loop residues Ser58-Ile64, (60-loop) which contact the isoalloxazine by over 0.35 nm, and by a small, displacement of the isoalloxazine moiety. The 60-loop movement away from, the flavin increases the solvent exposure of the flavin-binding site. The, conformation of the site at which 5'-phosphate of FMN normally binds is, similar in the two complexes, but in the riboflavin complex a sulphate or, phosphate ion from the crystallization buffer occupies the space. This, causes small structural perturbations in the phosphate-binding site. The, flexibility of the 60-loop in D. vulgaris flavodoxin appears to be a, contributing factor to the binding of riboflavin by the apoprotein, and a, feature that distinguishes the protein from other 'short chain', flavodoxins. In the absence of the terminal phosphate group, free movement, at the 5'-OH group of the ribityl chain can occur. Thus, the 5'-phosphate, of FMN secures the cofactor at the binding site and positions it, optimally. The structural changes which occur in the 60-loop in the, riboflavin complex probably account for most of the positive shift that is, observed in the midpoint potential of the semiquinone/hydroquinone couple, of the riboflavin complex compared to that of the FMN complex.
About this Structure
1BU5 is a Single protein structure of sequence from Desulfovibrio vulgaris with SO4 and RBF as ligands. Full crystallographic information is available from OCA.
Reference
X-ray crystal structure of the Desulfovibrio vulgaris (Hildenborough) apoflavodoxin-riboflavin complex., Walsh MA, McCarthy A, O'Farrell PA, McArdle P, Cunningham PD, Mayhew SG, Higgins TM, Eur J Biochem. 1998 Dec 1;258(2):362-71. PMID:9874201
Page seeded by OCA on Tue Nov 20 11:55:25 2007
