Electron Transfer to Hydroxylase through Component Interactions in Soluble Methane Monooxygenase

Area of Science:

• Environmental microbiology
• Biochemistry
• Enzyme kinetics

Background:

• Methane hydroxylation is critical due to methane's high heat capacity compared to CO2.
• Soluble methane monooxygenase (sMMO) facilitates methane oxidation, involving hydroxylase (MMOH), regulatory component (MMOB), and reductase (MMOR).
• The electron transfer pathway between MMOH and MMOR is not fully elucidated.

Purpose of the Study:

• To investigate the role of specific residues in the electron transfer pathway of sMMO from Methylosinus sporium 5.
• To understand the interaction between MMOH and MMOR, focusing on the ferredoxin domain of MMOR.

Main Methods:

• Purification of sMMO and hydroxylase from Methylosinus sporium 5.
• Site-directed mutagenesis of key tyrosine residues (Tyr93, Tyr95) in the MMOR ferredoxin domain.
• Biochemical assays to measure enzyme activity, FAD and iron ion concentrations, and binding affinities (Kd) between hydroxylase and mutated reductases.

Main Results:

• Mutational studies revealed changes in FAD and iron ion concentrations.
• Specific enzyme activities were significantly reduced in the MMOR-Y93A mutant.
• Binding affinities between hydroxylase and mutated reductases remained largely unchanged.

Conclusions:

• Tyrosine 93 (Tyr93) in the MMOR ferredoxin domain is a critical residue for efficient electron transfer.
• Tyr93 plays a key role in the electron transfer route at the MMOH-MMOR interface, affecting catalytic activity without significantly altering binding affinity.