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How Does Protein Architecture Facilitate the Transduction of ATP Chemical-Bond Energy into Mechanical Work? The Cases of Nitrogenase and ATP Binding-Cassette Proteins

Departments of Chemistry and Biochemistry, Duke University, Durham, North Carolina

Correspondence: Address reprint requests to Prof. David N. Beratan, Duke University, Dept. of Chemistry, 228C Gross Chem., Durham, NC 27708-0346. Tel.: 919-660-1526; E-mail: david.beratan{at}duke.edu.

Transduction of adenosine triphosphate (ATP) chemical-bond energy into work to drive large-scale conformational changes is common in proteins. Two specific examples of ATP-utilizing proteins are the nitrogenase iron protein and the ATP binding-cassette transporter protein, BtuCD. Nitrogenase catalyzes biological nitrogen fixation whereas BtuCD transports vitamin B₁₂ across membranes. Both proteins drive their reactions with ATP. To interpret how the mechanical force generated by ATP binding and hydrolysis is propagated in these proteins, a coarse-grained elastic network model is employed. The analysis shows that subunits of the proteins move against each other in a concerted manner. The lowest-frequency modes of the nitrogenase iron protein and of the ATP binding-cassette transporter BtuCD protein are found to link the functionally critical domains, and these modes are suggested to be responsible for (at least the initial stages) large-scale ATP-coupled conformational changes.