The Binding of Riboflavin-5′-Phosphate in a Flavoprotein: Flavodoxin at 2.0-Å Resolution

The crystal structure of the oxidized form of flavodoxin from Desulfovibrio vulgaris has been studied at 2.0-A resolution, and a detailed description of the region around the flavin mononucleotide binding site is now available. The flavin is between a tyrosine group, roughly parallel to it on one side, and a tryptophan, about 45 degrees from being parallel, on the other side. The two carbonyl groups and two nitrogen atoms of the flavin are hydrogen bonded to the peptide chain of the protein, while the two methyl groups are exposed at the surface of the protein. The phosphate group of the flavin mononucleotide is inside the protein and extensively hydrogen bonded to it. The ribityl group is hydrogen bonded both to the protein and to water on the surface of the protein.