Cloning, sequencing and structural analysis of membrane‐bound polyphenol oxidase from Granny Smith apples (Malus × domestica Borkh)

Abstract

SummaryThe gene sequence coding for the membrane‐bound polyphenol oxidase (mPPO) with a length of 1761 bp was cloned by PCR method and shown to contain one highly conserved sequence encoding a di‐copper‐binding region. The predicted three‐dimensional structure of mPPO indicated that the active site was located near two copper ions and composed of a typical bundle of four α‐helices. Each of the two catalytic copper ions was coordinated with three histidine residues in the hydrophobic pocket, yielding His 180, His 201, His 210, His 332, His 336 and His 366. Docking studies showed that 4‐methylcatechol and chlorogenic acid have different binding models due to different ligand sizes and binding sites in the active centre, and it was found that the smaller compound exhibited a higher affinity for mPPO. Molecular dynamic simulation results indicated that Phe 353 is important in controlling enzymatic activity through influencing substrate coordination in the active site.