Crystallographic characterization of flavodoxin from Anacystis nidulans

Abstract

Flavodoxin isolated from the blue-green alga, Anacystis nidulans, crystallizes from ammonium sulfate in space group P212121, with a = 57.08 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. nidulans protein, along with the near-isomorphism of crystals of the three oxidation states, distinguish this crystalline flavodoxin from the corresponding proteins of Clostaridium MP and Desulfovibrio vulgaris, whose three-dimensional structures are known. In contrast to Clostridium flavodoxins, but like the D. vulgaris protein, A. nidulans flavodoxin is capable of binding riboflavin in place of flavin mononucleotide (Ka = 2 x 106m-1).