Mechanical coupling in the nitrogenase complex.

Area of Science:

• Biochemistry and Molecular Biology
• Enzymology
• Structural Biology

Background:

• Nitrogenase is a crucial enzyme that converts atmospheric dinitrogen (N2) to ammonia (NH3).
• Mo-dependent nitrogenase functions as a dimer, comprising Fe Protein and MoFe protein components.
• Electron transfer and ATP hydrolysis are tightly coupled and regulated by an allosteric network.

Purpose of the Study:

• To analyze the mechanical coupling within the nitrogenase complex using graph theory.
• To understand the dynamics of allosteric regulation in nitrogen reduction.
• To identify key protein regions involved in inter- and intra-subunit communication.

Main Methods:

• Graph theory analysis applied to the mechanical coupling of the nitrogenase complex.
• Computational predictions of mechanically coupled regions.
• Validation using hydrogen-deuterium exchange mass spectrometry to study solution dynamics.

Main Results:

• Identified large-scale, correlated motions in regions near active sites, facilitating communication.
• Validated computational predictions against experimental solution dynamics data.
• Detailed specific couplings: Fe protein switch regions to [4Fe-4S] cluster, switch regions to MoFe protein β-188Ser loop, and inter-Fe protein P-loops.

Conclusions:

• Mechanical coupling is essential for allosteric regulation and efficient electron transfer in nitrogenase.
• The loop containing β-188Ser adjacent to the P-cluster plays a critical role in inter-half communication.
• Understanding these dynamics provides insights into the mechanism of nitrogen reduction.