S-Adenosyl-S-carboxymethyl-L-homocysteine

A novel cofactor is not something that is discovered every day, or even every year. So we are lucky this year. The crystal structure of a putative methyltransferase CmoA from Escherichia coli reveals the presence of [(3S)-3-amino-3-carboxypropyl]{[(2S,3S,4R,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methyl}(carboxymethyl)sulfanium, aka S-adenosyl-S-carboxymethyl-L-homocysteine, aka SCM-SAH [1—3]. Moreover, it was suggested that “a number of enzymes that have previously been annotated as SAM-dependent are in fact SCM-SAH-dependent” [1].

1. Byrne, R.T., Whelan, F., Aller, P., Bird, L.E., Dowle, A., Lobley, C.M., Reddivari, Y., Nettleship, J.E., Owens, R.J., Antson, A.A. and Waterman, D.G. (2013) S-Adenosyl-S-carboxymethyl-L-homocysteine: a novel cofactor found in the putative tRNA-modifying enzyme CmoA. Acta Crystallographica D69, 1090—1098.
2. PDB:4GEK
3. PDB:4IWN