Reconstitution of monomethylamine:Coenzyme M methyl transfer with a corrinoid protein and two methyltransferases purified from Methanosarcina barkeri

Methanogenesis from methylamines requires the intermediate methylation of 2-mercaptoethanesulfonate (CoM). In vitro reconstitution of CoM methylation with monomethylamine was achieved with three purified proteins: a monomethylamine corrinoid protein (MMCP), the ''A'' isozyme of methylcobamide:CoM methyltransferase (MTS-A), and a newly isolated protein termed monomethylamine methyltransferase (MMAMT). MMAMT is a 170-kDa protein with 52-kDa subunits. The MMAMT polypeptide was rate-limiting for methyl transfer until at a 2-fold molar excess over MMCP. MMAMT is a monomethylamine:MMCP methyltransferase, since methylation of MMCP required MMAMT but not MTS-A. MMCP and MMAMT formed a complex detectable by size exclusion high pressure liquid chromatography. Methyl group transfer from methyl-MMCP to CoM was mediated by MTS-A since methyl iodide:CoM methyl transfer by MMCP and MTS-A did not require MMAMT. MTS-M, an isozyme of MTS-A, was inactive in MMCP-dependent methyl transfer. Immunodepletion of MMCP from the extract inhibited CoM methylation with monomethylamine but mot dimethylamine. Purified MMCP reconstituted activity in immunodepleted extracts. These results show that MMCP is the major corrinoid protein for methanogenesis from monomethylamine detectable in extracts and that it interacts with two methyltransferases. MMAMT functions as a MMA: MMCP methyltransferase, while MTS-A functions as a methyl-MMCP:CoM methyltransferase.