Structure and function relationship of floral scent carboxyl methyltransferases

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The methyl esters methyl salicylate and methyl benzoate are volatile benzenoids (phenylpropanes) which are often found in floral scents. These structurally related compounds are synthesized by a new class of carboxyl methyltransferases, which is distinct from the well known type 1 and type 2 O methyltransferses. The identified enzymes from Clarkia breweri and Anthirrhinum majus are very substrate selective for either substrate, salicylic acid or benzoic acid, respectively. The enzyme specificity reflects the emission of methyl salicylale or methyl benzoate from both flowers, respectively. Carboxyl methyltransferases with a broader substrate acceptance are found in methyl salicylate and methyl benzoate emitting flowers, such as S.floribunda and N. suaveolens. The goal of this research project is to decipher the structure-function relationship of respective benzenoid carboxyl methyltransferases, e.g. determination of amino acids within and outside the active pocket that play a role in substrate preference and enzymatic features. Enzymes will be created by site directed mutagenesis strategy and isolated from paralogous and orthologous genes to analyse them biochemically, enzymatically and structurally. Differences in scent composition may also be a consequence of the expression of the methyltransferase genes and/or metabolic background of the tissue; an aspect that also will be addressed.