Tetramethylammonium:coenzyme M methyltransferase system from methanococcoides sp

Area of Science:

• Microbiology
• Biochemistry
• Archaea

Background:

• A novel methanogen, strain NaT1, belonging to the Methanosarcinaceae family, utilizes tetramethylammonium as its sole energy source.
• This organism offers a unique model for studying methylamine metabolism in archaea.

Purpose of the Study:

• To investigate the biochemical pathway and enzymes responsible for tetramethylammonium metabolism in strain NaT1.
• To identify and characterize the proteins involved in the formation of methyl-coenzyme M from tetramethylammonium.

Main Methods:

• Isolation and cultivation of methanogen strain NaT1.
• Enzymatic assays using cell extracts and purified proteins.
• Anoxic chromatography (DEAE-Sepharose) for protein fractionation.
• Protein purification and N-terminal amino acid sequencing.
• Comparative sequence analysis.

Main Results:

• Cell extracts of strain NaT1 catalyze the formation of methyl-coenzyme M from tetramethylammonium and coenzyme M, dependent on Ti(III) citrate and ATP.
• Two key protein fractions (3 and 4) were identified as essential for this activity.
• A 50-kDa protein from fraction 4 and a 22-kDa corrinoid protein and a 40-kDa methylcobalamin:coenzyme M methyltransferase (MT2) from fraction 3 were purified.
• The 40-kDa protein showed sequence similarity to known MT2 isoenzymes.
• Tetramethylammonium:coenzyme M methyltransferase activity was absent when strain NaT1 was grown on trimethylamine.
• Strain NaT1 was identified as Methanococcoides, closely related to Methanococcoides methylutens.

Conclusions:

• Strain NaT1 possesses a specific enzymatic system for tetramethylammonium metabolism, distinct from trimethylamine metabolism.
• The identified proteins, including a novel methyltransferase, are crucial for methyl-coenzyme M synthesis from tetramethylammonium.
• This study elucidates a new metabolic capability within the Methanococcoides genus.