Cloning and characterization of a novel O-methyltransferase from Flammulina velutipes that catalyzes methylation of pyrocatechol and pyrogallol structures in polyphenols

Abstract

A novel O-methyltransferase gene was isolated from Flammulina velutipes. The isolated full-length cDNA was composed of a 690-nucleotide open reading frame encoding 230 amino acids. A database search revealed that the deduced amino acid sequence was similar to those of other O-methyltransferases; the highest identity was only 61.8% with Laccaria bicolor. The recombinant enzyme was expressed by Escherichia coli. BL21 (DE3) was assessed for its ability to methylate (−)-epigallocatechin-3-O-gallate (EGCG). LC–TOF–MS and NMR revealed that the enzyme produced five kinds of O-methylated EGCGs: (−)-epigallocatechin-3-O-(3-O-methyl)gallate, (−)-epigallocatechin-3-O-(4-O-methyl)gallate, (−)-epigallocatechin-3-O-(3,4-O-dimethyl)gallate, (−)-epigallocatechin-3-O-(3,5-O-dimethyl)gallate, and (−)-4′-O-methylepigallocatechin-3-O-(3,5-O-dimethyl)gallate. The substrate specificity of the enzyme for 20 kinds of polyphenols was assessed using the crude recombinant enzyme of O-methyltransferase. This enzyme introduced methyl group(s) into polyphenols with pyrocatechol and pyrogallol structures.

Graphical Abstract

Chemical structures that can and cannot be catalyzed by Fv-OMT. Pyrogallol and pyrocatechol were recognized, whereas resorcinol, phloroglucinol, and phenol were not.

Key words:

• Flammulina velutipes
• O-methyltransferase
• O-methylated EGCGs
• O-methylated polyphenols

Notes

Abbreviations: EGCG, (−)-epigallocatechin-3-O-gallate; EGCG3″Me, (−)-epigallocatechin-3-O-(3-O-methyl)gallate; EGCG4″Me, (−)-epigallocatechin-3-O-(4-O-methyl)gallate; EGCG3″,5″diMe, (−)-epigallocatechin-3-O-(3,5-O-dimethyl)gallate; EGCG3″,4″diMe, (−)-epigallocatechin-3-O-(3,4-O-dimethyl)gallate; EGCG4′,3″,5″triMe, (−)-4′-O-methylepigallocatechin-3-O-(3,5-O-dimethyl)gallate; SAM, S-adenosyl-L-methionine; CCoAOMT, Caffeoyl-coenzyme A O-methyltransferase.