A single amino acid substitution alters the vanillylamine synthesis activity of Capsicum pAMT

Some Capsicum synthesize a unique pungent alkaloid called capsaicin in their fruits. In the synthetic pathway of capsaicin, vanillylamine is produced from vanillin in a reaction catalyzed by a putative aminotransferase (pAMT). Therefore, the capsaicinoids content in the fruits is thought to partially depend on the characteristics of pAMT. Comparing Yume-matsuri (yume), C. annuum variety, and red habanero (RH), C. chinense variety, the vanillylamine synthesis activity of the placental extract was higher in yume than in RH. When each recombinant pAMT (rpAMT) was generated using the Escherichia coli expression system and their activities were compared, yume rpAMT synthesized 14-fold more vanillylamine than RH rpAMT. The amino acid sequence of yume and RH pAMT deduced from the cDNAs revealed that only 7 of 459 residues differed. When a single amino acid residue–substituted rpAMT was generated in which the 56th amino acid was swapped with one other, the amount of vanillylamine synthesis of yume and RH rpAMTs was inverted. Furthermore, it was suggested that the 56th amino acid contributed to the affinity for the coenzyme pyridoxal phosphate. Differences in the vanillylamine synthesis activity of pAMT may also lead to differences in the amount of capsaicin synthesis that accumulates in the fruit. Since capsaicin is a compound with commercial value, this finding may provide new insights into the creation of a variety that can synthesize more capsaicin.