Borneol dehydrogenase from Pseudomonas sp. TCU-HL1 possesses novel quinuclidinone reductase activities

Abstract

Borneol dehydrogenase (BDH) catalyses the last step of the camphor biosynthetic pathway in plants and the first reaction in the borneol degradation pathway in soil microorganisms. Native or engineered BDH can be used to produce optically pure borneol and camphor. The recently reported apo-form crystal structure of BDH (PDB ID: 6M5N) from Pseudomonas sp. TCU-HL1 superimposes well with that of 3-quinuclidinone reductase (QR) (PDB ID: 3AK4) from Agrobacterium tumefaciens. QR catalyses the conversion of 3-quinuclidinone into (R)-3-(−)-quinuclidinol, an important chiral synthone for several drugs. However, the kinetic parameter, kcat , of QR was not determined in the previous reports even though both BDH and QR have various potential industrial applications. Here, we aimed to further characterise their structural and functional relationship. Recombinant QR with the native sequence was cloned, expressed in E. coli, and purified. We found that 3-quinuclidinone can be used as an alternative substrate for BDH. Only (R)-3-(−)-quinuclidinol was detected in this BDH-catalysed reaction. The results of 3 D molecular docking simulation show that 3-quinuclidinone and (+)-/(-)- borneol were docked to two different parts of the QR active site. In contrast, all three compounds are docked uniformly to the alpha-1 helix of BDH. There results explain why BDH can turnover 3-quinuclidinone, while QR can not act on (+)-/(-)-borneol.