The Role of Methionine 156 in Cross-subunit Nucleotide Interactions in the Iron Protein of Nitrogenase

摘要: A variant Fe protein has been created at the completely conserved residue methionine 156 by changing it to cysteine. The Azotobacter vinelandii strain expressing M156C is unable grow under nitrogen-fixing conditions, and purified cannot support substrate reduction in vitro. This mutation an effect on protein's ability undergo MgATP-induced conformational change as evidenced fact that chelated presence of MgATP with a lower observed rate than wild-type. While electron paramagnetic resonance spectra this are similar those wild-type protein, circular dichroism spectrum markedly different MgATP, showing conformation adopted following nucleotide binding from conformation. Although competition activity chelation assays show can still form complex MoFe altered only supports hydrolysis 1% protein. model based x-ray crystallographic information presented explain importance Met-156 stabilization correct via critical interactions Asp-43 other subunit.