Crystallographic characterization of flavodoxin from Anacystis nidulans.

Flavodoxin isolated from the blue-green alga, Anmyatis nidulana, crystallizes from ammonium sulfate in space group P2,2,2,, wwith a = 67.08 A, b = 69.24 A and c = 45.55 A. The diffraction patterns extend to a resolution of at least 1.8 A. Reduction of the flavin mononucleotide in the crystalline protein, to either the semi-quinone or fully reduced (hydroquinone) state, results in minimal changes in cell dimensions and diffracted intensities. The higher molecular weight (19,000 to 20,000) and spectral properties of the A. nidulana protein, along with the near-isomorphism of crystals of the three oxidation states, distinguish this crystalline flavodoxin from the corresponding proteins of Cloetidium MP and Deaulfovibrio vuJgaris, whose three-dimensional structures are known. In contrast to Clorrtridiurn flavodoxins, but like the D. ~a& protein, A. nidulana flavodoxin is capable of binding riboflavin in place of flavin mononucleotide (K, = 2x loem-‘).