Didehydroaspartate Modification in Methyl-Coenzyme M Reductase Catalyzing Methane Formation

Area of Science:

• Biochemistry
• Microbiology
• Structural Biology

Background:

• Methanogenic and methanotrophic archaea utilize methyl-coenzyme M reductase (MCR) for methane metabolism.
• MCR contains the nickel porphinoid F430 and conserved amino acid residues near its active site.

Purpose of the Study:

• To identify novel post-translational modifications in MCR.
• To elucidate the structural and functional significance of these modifications.

Main Methods:

• Mass spectrometry was employed to detect and identify modified amino acids.
• High-resolution X-ray crystallography provided detailed structural insights into the MCR active site.
• Chemical reduction was used to assess the stability and reactivity of the novel residue.

Main Results:

• A novel post-translationally modified amino acid, didehydroaspartate, was identified adjacent to a thioglycine residue in MCR.
• Didehydroaspartate was detected in MCR from Methanothermobacter marburgensis and Methanosarcina barkeri.
• This residue was absent in MCR from Methanothermobacter wolfeii, indicating it is not essential for all MCR activity.

Conclusions:

• Didehydroaspartate is a newly discovered component of the MCR active site in certain archaea.
• Its presence suggests a potential role in fine-tuning MCR catalytic efficiency.
• The dispensability of didehydroaspartate highlights evolutionary flexibility in archaeal methane metabolism.