The known members of plant methyl esterase (MES) family catalyze the hydrolysis of a C-O ester linkage of methyl esters of several phytohormones including indole-3-acetic acid, salicylic acid and jasmonic acid. The genome of grapevine (Vitis vinifera) was found to contain 15 MES genes, designated VvMES1-15. In this report, VvMES5 was selected for molecular, biochemical and structural studies. VvMES5 is most similar to tomato methyl jasmonate esterase. E. coli-expressed recombinant VvMES5 displayed methyl jasmonate (MeJA) esterase activity, it was renamed VvMJE1. Under steady-state conditions, VvMJE1 exhibited an apparent Km value of 92.9 μM with MeJA. VvMJE1 was also shown to have lower activity with methyl salicylate (MeSA), another known substrate of the MES family, and only at high concentrations of the substrate. To understand the structural basis of VvMJE1 in discriminating MeJA and MeSA, a homolog model of VvMJE1 was made using the X-ray structure of tobacco SABP2, which encodes for methyl salicylate esterase, as a template. Interestingly, two bulky residues at the binding site and near the surface of tobacco SABP2 are replaced by relatively small residues in VvMJE1. Such a change enables the accommodation of a larger substrate MeJA in VvMJE1. The expression of VvMJE1 was compared in control grape plants and grape plants treated with one of the three stresses: heat, cold and UV-B. While the expression of VvMJE1 was not affected by heat treatment, its expression was significantly up-regulated by cold treatment and UV-B treatment. This result suggests that VvMJE1 has a role in response of grape plants to these two abiotic stresses.
Keywords: Abiotic stress; Grapevine; Homology modelling; Methyl jasmonate; Methylesterase.
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