[Cloning and functional verification of carboxyl CoA ligases(AeCCLs) in Arnebia euchroma]

Carboxyl CoA ligases(CCLs) is an important branch of adenylate synthetase gene family, which mainly has two-step catalytic reactions. Firstly, in the presence of adenosine triphosphate, it can catalyze the pyrophosphorylation of carboxylateswith diffe-rent structures to form corresponding acyl adenosine monophosphate intermediates. Secondly, adenosine monophosphate was replaced by free electrons in the mercaptan group of enzyme A or other acyl receptors by nucleophilic attack to form thioesters. In this study, on the basis of the transcriptome database of Arnebia euchroma, two genes were selected, named AeCCL5(XP_019237476.1) and AeCCL7(XP_019237476.1). Bioinformatics analysis showed that their relative molecular weights were 60.569 kDa and 60.928 kDa, theoretical PI were 8.59 and 8.92, respectively. They both have transmembrane domains but without signal peptide. By multiple sequence alignment and phylogenetic tree analysis, we found that the similarity between AeCCLs and other plant homologous proteins was not high, and the substrate binding sites of AeCCLs were not highly conserved. The reasons might be that the sequence and structure need to adapt to the changes of new substrates in the process of evolution. In this study, the full-length of AeCCL5 and AecCCL7 were cloned into the expression vector pCDFDuet-1. The proteins of AeCCL5 and AeCCL7 with His-tag were expressed in Escherichia coli. The proteins of AeCCL5 and AeCCL7 were purified by nickel column. In vitro enzymatic reactions proved that both AeCCL5 and AeCCL7 can participate in the upstream phenylpropane pathway of shikonin biosynthesisby catalyzing 4-coumaric acid to produce 4-coumarin-CoA, and then to synthesis p-hydroxybenzoic acid, which is an important precursor of shikonin biosynthesis in A. euchroma.