A short-chain dehydrogenase involved in terpene metabolism from Zingiber zerumbet

The rhizome oil of Zingiber zerumbet Smith contains an exceptionally high content of sesquiterpenoids with zerumbone, a predominating potential multi-anticancer agent. Biosynthetic pathways of zerumbone have been proposed, and two genes ZSS1 and CYP71BA1 that encode the enzymes catalyzing the first two steps have been cloned. In this paper, we isolated a cDNA clone (ZSD1) that encodes an alcohol dehydrogenase capable of catalyzing the final step of zerumbone biosynthesis. ZSD1 has an open reading frame of 804 bp that encodes a 267-residue enzyme with a calculated molecular mass of 28.7 kDa. After expression in Escherichia coli, the recombinant enzyme was found to catalyze 8-hydroxy-alpha-humulene into zerumbone. ZSD1 is a member of the short-chain dehydrogenase/reductase superfamily (SDR) and shares high identities with other plant SDRs involved in secondary metabolism, stress responses and phytosteroid biosynthesis. In contrast to the transcripts of ZSS1 and CYP71BA1, which are almost exclusively expressed in rhizomes, ZSD1 transcripts are detected in leaves, stems and rhizomes, suggesting that ZSD1 may also be involved in other biological processes. Consistent with its proposed flexible substrate-binding pocket, ZSD1 also converts borneol to camphor with K-m and k(cat) values of 22.8 mu M and 4.1 s(-1), displaying its bisubstrate feature.