CRYSTAL-STRUCTURE OF THE FLAVOHEMOGLOBIN FROM ALCALIGENES-EUTROPHUS AT 1.75 ANGSTROM RESOLUTION

The molecular structure of the flavohemoglobin from Alcaligenes eutrop hus has been determined to a resolution of 1.75 Angstrom and refined t o an R-factor of 19.6%, The protein comprises two fused modules: a hem e binding module, which belongs to the globin family, and an FAD bindi ng oxidoreductase module, which adopts a fold like ferredoxin reductas e. The most striking deviation of the bacterial globin structure from those of other species is the movement of helix E in a way to provide more space in the vicinity of the distal heme binding site, A comparis on with other members of the ferredoxin reductase family shows similar tertiary structures for the individual FAD and NAD binding domains bu t largely different interdomain orientations, The heme and FAD molecul es approach each other to a minimal distance of 6.3 Angstrom and adopt an interplanar angle of 80 degrees, The electron transfer from FAD to heme occurs in a predominantly polar environment and may occur direct ly or be mediated by a water molecule.