Crystal structure and enantioselectivity of terpene cyclization in SAM-dependent methyltransferase TleDYu, F., Li, M.J., Xu, C.Y., Sun, B., Zhou, H., Wang, Z.J., Xu, Q., Xie, M.Y., Zuo, G., Huang, P., Guo, H., Wang, Q.S., He, J.H.
(2016) Biochem.J. 473: 4385-4397
- PubMed: 27613858
- DOI: 10.1042/BCJ20160695
- Primary Citation of Related Structures:  5GM2
- PubMed Abstract:
TleD is a SAM (S-adenosyl-l-methionine)-dependent methyltransferase and acts as one of the key enzymes in the teleocidin B biosynthesis pathway. Besides methyl transferring, TleD also rearranges the geranyl and indole moieties of the precursor to for ...
TleD is a SAM (S-adenosyl-l-methionine)-dependent methyltransferase and acts as one of the key enzymes in the teleocidin B biosynthesis pathway. Besides methyl transferring, TleD also rearranges the geranyl and indole moieties of the precursor to form a six-membered ring. Moreover, it does not show homologies with any known terpenoid cyclases. In order to elucidate how such a remarkable reaction could be achieved, we determined the complex crystal structures of TleD and the cofactor analogue S-adenosyl-l-homocysteine with or without the substrate teleocidin A1. A domain-swapped pattern via an additional N-terminal α-helix is observed in TleD hexamers. Structural comparison and alignment shows that this additional N-terminal α-helix is the common feature of SAM methyltransferase-like cyclases TleD and SpnF. The residue Tyr21 anchors the additional N-terminal α-helix to a 'core SAM-MT fold' and is a key residue for catalytic activity. Molecular dynamics simulation results suggest that the dihedral angle C23-C24-C25-C26 of teleocidin A1 is preferred to 60-90° in the TleD and substrate complex structure, which tend to adopt a Re-face stereocenter at C25 position after reaction and is according to in vitro enzyme reaction experiments. Our results also demonstrate that methyl transfer can be a new chemical strategy for carbocation formation in the terpene cyclization, which is the key initial step.
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhang Heng Road, Pudong New District, Shanghai 201203, P.R. China.