Structure and function relationship of floral scent carboxyl methyltransferases

水杨酸甲酯和苯甲酸甲酯是挥发性苯类化合物(苯丙烷)，常见于花香中。这些结构上相关的化合物是由一类新的羧甲基转移酶合成的，这与众所周知的1型和20型甲基转移不同。已鉴定的短毛克氏杆菌和大响鱼的酶分别对底物、水杨酸或苯甲酸都有很强的底物选择性。酶的专一性分别反映了两朵花释放的水杨酸甲酯或苯甲酸甲酯。在水杨酸甲酯和苯甲酸甲酯中发现了底物接受性更广的羧甲基转移酶。这项研究的目标是破译各自苯类羧甲基转移酶的结构-功能关系，例如测定活性口袋内和活性口袋外的氨基酸对底物偏好和酶特性起作用。酶将通过定点突变策略产生，并从同源和同源基因中分离出来，进行生化、酶和结构分析。气味成分的差异也可能是甲基转移酶基因表达和/或组织代谢背景的结果；这一方面也将得到解决。

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.