Abstract
Delphinidin 3-(6''-malonyl)glucoside-3',5'-diglucoside-6'''-p-coumaroyltransferase (3'AT) has been assigned to a role in conversion of ternatin C5 into ternatin C3. This enzyme activity was detected for the first time from the petals of butterfly pea using 1-O-acylglucose as acyl-donor. The purified 3'AT had heteromeric structure comprised of 31- and 24-kDa subunits on SDS-PAGE. Biochemical and enzymatic characters suggested that 3'AT was a kind of 1-O-acylglucose-dependent acyltransferases which constitute a class of serine carboxypeptidase-like acyltransferase (SCPL-AT). We employed a PCR-based strategy using primers designed on conserved regions of SCPL proteins to clone the gene. The isolated cDNA clone, CtAT1, encoded 31- and 24-kD subunits containing the sequences for three tryptic fragments derived from purified 3'AT protein. The cDNA encoded a SCPL protein with a N-terminal signal sequence, three possible N-glycosylation sites, and Ser-His-Asp putative catalytic triad. Expression of the cDNA in a baculovirus expression vector produced an active protein displaying 1-O-acylglucose:anthocyanin 3'-O-glucoside-O-acyltransferase activity.
