This family is an aTrm56 that catalyses the 2'-O-methylation of the cytidine residue in archaeal tRNA, using S-adenosyl-L-methionine. Biochemical assays showed that aTrm56 forms a dimer and prefers the L-shaped tRNA to the lambda form as its substrate [1] [2]. aTrm56 consists of the SPOUT domain, which contains the characteristic deep trefoil knot for AdoMet binding, and a unique C-terminal beta-hairpin [3].

1: The Cm56 tRNA modification in archaea is catalyzed either by a specific 2'-O-methylase, or a C/D sRNP. Renalier MH, Joseph N, Gaspin C, Thebault P, Mougin A; RNA. 2005;11:1051-1063. PMID:15987815

2: Two different mechanisms for tRNA ribose methylation in Archaea: a short survey. Clouet-d'Orval B, Gaspin C, Mougin A; Biochimie. 2005;87:889-895. PMID:16164996

3: Crystal structure and mutational study of a unique SpoU family archaeal methylase that forms 2'-O-methylcytidine at position 56 of tRNA. Kuratani M, Bessho Y, Nishimoto M, Grosjean H, Yokoyama S; J Mol Biol. 2008;375:1064-1075. PMID:18068186