Nitrogenase Complexes: Multiple Docking Sites for a Nucleotide Switch Protein
Adenosine triphosphate (ATP) hydrolysis in the nitrogenase complex controls the cycle of association and dissociation between the electron donor adenosine triphosphatase (ATPase) (Fe-protein) and its target catalytic protein (MoFe-protein), driving the reduction of dinitrogen into ammonia. Crystal structures in different nucleotide states have been determined that identify conformational changes in the nitrogenase complex during ATP turnover. These structures reveal distinct and mutually exclusive interaction sites on the MoFe-protein surface that are selectively populated, depending on the Fe-protein nucleotide state. A consequence of these different docking geometries is that the distance between redox cofactors, a critical determinant of the intermolecular electron transfer rate, is coupled to the nucleotide state. More generally, stabilization of distinct docking geometries by different nucleotide states, as seen for nitrogenase, could enable nucleotide hydrolysis to drive the relative motion of protein partners in molecular motors and other systems.
Additional Information© 2005 American Association for the Advancement of Science. 2 June 2005; Accepted 1 August 2005. This work was supported by the NIH and HHMI. F.A.T. acknowledges the Helen Hay Whitney Foundation for a postdoctoral fellowship. Operations at Stanford Synchrotron Radiation Laboratory and the Advanced Light Source are funded by the Office of Basic Energy Sciences of the U.S. Department of Energy and NIH. We thank the Parsons and Moore Foundations for support of facilities at Caltech. Coordinates and structure factors for the nf-Av2:Av1, adp-Av2:Av1, and pcp-Av2:Av1 structures have been deposited in the RCSB Protein Data Bank (entries 2AFH, 2AFI, and 2AFK, respectively) for release upon publication.
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