4kec

Publication Abstract from PubMed

Hydroxycinnamoyltransferase (SbHCT) from Sorghum bicolor participates in an early step of the phenylpropanoid pathway, exchanging CoA esterified to p-coumaric acid with shikimic or quinic acid, as intermediates in the biosynthesis of the monolignols coniferyl acohol and sinapyl alcohol. In order to elucidate the mode of action of this enzyme, we have determined the crystal structures of SbHCT in its apo-form and ternary complex with shikimate and p-coumaroyl CoA, which was converted to its product during crystal soaking. The structure revealed the roles of Thr36, Ser38, Tyr40, His162, Arg371 and Thr384 in catalysis and specificity. Based on the exact chemistry of p-coumaroyl CoA and shikimic acid in the active site and analysis of kinetic and thermodynamic data of wild-type and mutants, we propose a role for His162 and Thr36 in the catalytic mechanism of HCT . Considering the calorimetric data, substrate binding of SbHCT should occur sequentially, with p-coumaroyl CoA binding prior to the acyl acceptor molecule. While some HCT's can use both shikimate and quinate as an acyl acceptor, SbHCT displays low activity toward quinate. Comparison of the structure of Sorghum HCT with the HCT involved in chlorogenic acid synthesis in coffee (Coffea canephora) revealed many shared features. Taken together, these observations explain how CoA-dependent transferases with similar structural features can participate in different biochemical pathways across species.

Elucidation of the structure and reaction mechanism of Sorghum bicolor hydroxycinnamoyltransferase and its structural relationship to other CoA-dependent transferases and synthases.,Walker AM, Hayes RP, Youn B, Vermerris W, Sattler SE, Kang C Plant Physiol. 2013 Apr 26. PMID:23624856^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.