Negative cooperativity in the nitrogenase Fe protein electron delivery cycle

Area of Science:

• Biochemistry
• Enzymology
• Nitrogen Fixation

Background:

• Nitrogenase facilitates ATP-dependent reduction of N2 to NH3.
• The enzyme comprises MoFe and Fe proteins, with electron transfer (ET) occurring between them.
• The Fe protein cycle involves ATP binding, association with MoFe protein, ET, ATP hydrolysis, and dissociation.

Purpose of the Study:

• To investigate the functional independence of the two active sites in the MoFe protein during the Fe protein cycle.
• To elucidate the mechanism of electron transfer and ATP hydrolysis in nitrogenase.

Main Methods:

• Quantitative kinetic measurements of electron transfer, ATP hydrolysis, and P(i) release.
• Pre-steady-state kinetic analysis of the nitrogenase complex.
• Normal-mode calculations to analyze protein motions.

Main Results:

• The two halves of the MoFe protein do not operate independently during the Fe protein cycle.
• Kinetic data fit a negative-cooperativity model, where activity in one half influences the other.
• Normal-mode analysis suggests correlated motions between the two halves, indicating potential communication pathways.

Conclusions:

• The Fe protein cycle exhibits negative cooperativity between the two active sites of the MoFe protein.
• Communication between the MoFe protein halves is crucial for efficient nitrogenase function.
• Protein dynamics may mediate inter-site communication in nitrogenase.