PMID:9874201

Citation	Walsh, MA, McCarthy, A, O'Farrell, PA, McArdle, P, Cunningham, PD, Mayhew, SG and Higgins, TM (1998) X-ray crystal structure of the Desulfovibrio vulgaris (Hildenborough) apoflavodoxin-riboflavin complex. Eur. J. Biochem. 258:362-71
Abstract	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.
Links	PubMed
Keywords	Apoproteins/chemistry; Binding Sites; Crystallography, X-Ray; Desulfovibrio vulgaris/chemistry; Flavin Mononucleotide/chemistry; Flavodoxin/chemistry; Hydrogen Bonding; Models, Molecular; Molecular Sequence Data; Oxidation-Reduction; Phosphates/metabolism; Protein Conformation; Protein Structure, Secondary; Riboflavin/chemistry
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
DESVH:FLAV		GO:0009055: electron carrier activity	ECO:0000314:		F		Figure 4 of the article shows a stereo view of supercomposition held between the apoflavodoxin flavin-binding site in the FMN and the riboflavin complexes. The similar structures provide evidence of flavodoxin found in D. vulgaris. Additionally, figure 5 in the article provides a schematic representation of how hydrogen bonding takes place at both the flavin-binding site of apoflavodoxin and the riboflavin complex. The structures have a similar core but are only reversed at the Tyr-100 site, providing further evidence of the presnce of flavodoxin. Page 367 in the article further provides evidence by stating that "the interactions of the 90-loop in the structure of the apoflavodoxin-riboflavin complex are essentially identical to those in native flavodoxin, differing only in the orientation of the isoalloxazine and the interactions with Y98."	complete CACAO 12081

References

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