Catalyzes the 2'-O-methylation at nucleotide C2498 in 23S rRNA. Modifies C2498 in naked 23S rRNA, but not in assembled 50S subunits or ribosomes. cytidine(2498) in 23S rRNA + S-adenosyl-L-methionine = 2'-O-methylcytidine(2498) in 23S rRNA + H(+) + S-adenosyl-L-homocysteine Monomer. Consists of two structural domains: an N-terminal THUMP domain followed by a C-terminal catalytic Rossmann-like fold MTase domain in a novel arrangement. The two domains are connected by a long loop. Belongs to the class I-like SAM-binding methyltransferase superfamily. RNA methyltransferase RlmE family. RlmM subfamily.