Members of this family are about 220 amino acids long. It includes Rhamnosyl O-methyltransferase which catalyses the O-methylation of the hydroxyl group located on C-2 of the first rhamnosyl residue linked to the phenolic group of glycosylated phenolphthiocerol dimycocerosates (PGL) and p-hydroxybenzoic acid derivatives (p-HBAD) [3]. This entry also includes CmcI protein Swiss:O85726 which was previously presumed to represent the cephalosporin-7--hydroxylase [1]. However, it is apparently a methyltransferase that works with hydroxylase CmcJ, and its most likely function is to catalyse the transfer of a methyl group from SAM to the 7alpha-hydroxy cephalosporin in the second catalytic reaction of cephamycin formation. Studies using recombinant proteins purified from E. coli suggest that the complex, but not the separate proteins, exhibits a strong interaction with SAM and cephalosporin C [2].

1: Investigation of the Streptomyces clavuligerus cephamycin C gene cluster and its regulation by the CcaR protein. Alexander DC, Jensen SE; J Bacteriol 1998;180:4068-4079. PMID:9696752

2: Insights into cephamycin biosynthesis: the crystal structure of CmcI from Streptomyces clavuligerus. Oster LM, Lester DR, Terwisscha van Scheltinga A, Svenda M, van Lun M, Genereux C, Andersson I; J Mol Biol. 2006;358:546-558. PMID:16527306

3: Molecular dissection of the role of two methyltransferases in the biosynthesis of phenolglycolipids and phthiocerol dimycoserosate in the Mycobacterium tuberculosis complex. Perez E, Constant P, Laval F, Lemassu A, Laneelle MA, Daffe M, Guilhot C; J Biol Chem. 2004;279:42584-42592. PMID:15292265