Molecular sorting of nitrogenase catalytic cofactors

Area of Science:

• Biochemistry
• Microbiology
• Nitrogen Fixation

Background:

• Azotobacter vinelandii produces three nitrogenase isozymes: Mo-dependent, V-dependent, and Fe-only.
• These isozymes utilize distinct but similar metallocofactors: FeMo-cofactor, FeV-cofactor, and FeFe-cofactor.
• Proper cofactor assembly is crucial for nitrogenase function and preventing hybrid enzyme formation.

Purpose of the Study:

• To investigate the mechanism preventing incorrect cofactor incorporation into the Fe-only nitrogenase in Azotobacter vinelandii.
• To identify the protein responsible for maintaining the fidelity of the Fe-only nitrogenase system.

Main Methods:

• Investigated the role of the AnfO protein in Azotobacter vinelandii nitrogenase maturation.
• Characterized the interaction between AnfO domains and nitrogenase components.
• Assessed the binding capacity of AnfO for different metallocofactors.

Main Results:

• The AnfO protein, with its two domains, prevents misincorporation of FeMo- and FeV-cofactors into the Fe-only nitrogenase.
• The N-terminal domain of AnfO binds immature Fe-only nitrogenase, while the C-terminal domain captures incorrect cofactors.
• FeFe-cofactor assembly occurs within the catalytic partner, thus evading AnfO capture and ensuring Fe-only nitrogenase specificity.

Conclusions:

• AnfO acts as a molecular guardian, ensuring cofactor specificity for the Fe-only nitrogenase.
• This mechanism involves protein-protein interactions and metallocofactor binding for precise molecular sorting.
• Differential cofactor assembly pathways are exploited to maintain nitrogenase isozyme fidelity.