Adenosine dimethyltransferase

Function

Adenosine dimethyltransferase (KsgA) dimethylates two adjacent adenines at the C-terminal of the 16S rRNA in the small 30S ribosomal subunit, thus modifying it. KsgA catalyzes the dimethylation of adenines 1518-1519 using S-adenosyl-methionine (SAM) as the methyl donor and producing S-adenosyl-homocysteine (SAH).

Relevance

KsgA confers resistance to the antibiotic kasugomycin.

Structural highlights

Among methyltransferases, KsgA and the reaction it catalyzes are conserved throughout evolution. However, the specifics of substrate recognition by the enzyme remain unknown. Here we report structures of (SAH, reaction product of cofactor S-adenosylmethionine), revealing critical structural information on KsgA-RNA and KsgA-SAH interactions. Moreover, the structures show how conformational changes that occur upon RNA binding create the cofactor-binding site. There are nine conserved functional motifs (motifs I-VIII and X) in KsgA. Prior to RNA binding, motifs I and VIII are flexible, each exhibiting two distinct conformations. Upon RNA binding, the two motifs become stabilized in one of these conformations, which is compatible with the binding of SAH. Motif X, which is also stabilized upon RNA binding, is directly involved in the binding of SAH.^[1]

3D structures of adenosine dimethyltransferase

Adenosine dimethyltransferase 3D structures