Elucidation of a MgATP Signal Transduction Pathway in the Nitrogenase Iron Protein:  Formation of a Conformation Resembling the MgATP-Bound State by Protein Engineering†

摘要: The present work defines one MgATP signal transduction pathway in the nitrogenase iron (Fe) protein. Deletion of an amino acid (Leu 127) by site-directed mutagenesis protein chain between Asp 125, located ATP binding site, and Cys 132, a ligand to [4Fe-4S] cluster, resulted conformational changes resembling MgATP-bound state absence any bound nucleotides. Specifically, 1H nuclear magnetic resonance, electron paramagnetic circular dichroism spectroscopic properties, along with Fe chelation assays, suggested that deletion Leu 127 electronic properties cluster similar those normally observed upon wild-type lowered redox potential [4FE-4S] 112 mV compared wild-typeFe (-412mV -294 mV). A nearly identical lowering 120 occurs (-294 420 L127delta did not contain nucleotides which could account for changes. results support model from ASP 125 132 acts as suggests mechanism this cluster. was found still bind 2 or MgADP molecules/Fe Unlike protein, ADP Mg2+. Finally, MoFe although complex catalyze hydrolysis substrate reduction. In concurrence previous models, homologies switch II region broad class GTPase proteins (G-proteins) are discussed.