STRUCTURAL ANALYSIS OF METHYLKETONE SYNTHASE 1

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Medium length methylketones like 2-tridecanone and 2-undecanone are potent toxins to a number of herbivorous insects. The production of both 2-tridecanone and 2-undecanone was recently linked to the expression of a member of the alpha/beta hydrolase fold family of proteins, Methylketone Synthase 1 (MKS1). MKS1 is a plastid localized protein shown to catalyze the de-esterification of beta-myristoyl-ACP to beta-ketoacids. Proteins containing the alpha/beta hydrolase fold have little sequence identity but do possess a conserved catalytic triad of nucleophile, acid and a histidine in their active sites. Typically these residues consist of Ser, Asp, and His. Upon modeling MKS1 from Hydroxynitrile Lysase (HNL), also a member of the alpha/beta hydrolase superfamily, it was apparent that MKS1 did not contain the canonical catalytic triad. MKS1 crystals were obtained and the three dimensional structure was solved at 2.3 ¿ resolution by molecular replacement using HNL. From the crystal structure a highly stable H2O molecule was present within the MKS1 active site leading to the proposal that this H2O molecule could act as the nucleophile missing in MKS1. In order to address the proposed mechanism, higher resolution data of MKS1 in complex with substrate and or products is a requirement.