Mechanism of flavin mononucleotide cofactor binding to the Desulfovibrio vulgaris flavodoxin. 2. Evidence for cooperative conformational changes involving tryptophan 60 in the interaction between the phosphate- and ring-binding subsites

A mechanism has been proposed for the binding of flavin mononucleotide (FMN) and riboflavin to the apoflavodoxin from Desulfovibrio vulgaris [Murray, T. A., and Swenson, R. P. (2003) Biochemistry 42, 2307−2316]. In this model, the binding of the flavin isoalloxazine ring is dependent on the presence of a phosphate moiety in the phosphate-binding subsite, suggesting a cooperative interaction between that region and the ring-binding subsite. In the absence of inorganic phosphate, FMN can bind through the initial association of its 5‘-phosphate group in the phosphate-binding subsite followed by insertion of the flavin ring. Because riboflavin lacks the 5‘-phosphate group, it is unable to bind to this apoprotein in the absence of inorganic phosphate in solution. However, inorganic phosphate can enhance the rate of ring binding by occupying the phosphate-binding subsite. In this paper, NMR, near-UV circular dichroism (CD), and fluorescence spectroscopy provide evidence for a phosphate-induced conformational ch...