Biocatalytic methylation and demethylation via a shuttle catalysis concept involving corrinoid proteins

Judith E Farnberger,Ferdinand Zepeck,Sarah Bierbaumer,Katharina Hiebler,Nina Richter,Wolfgang Skibar,Wolfgang Kroutil,Mathias Pickl

doi:10.1038/s42004-018-0083-2

Abstract

Synthetically established methods for methylation of phenols and demethylation of methyl phenyl ethers rely in general on hazardous reagents or/and harsh reaction conditions and are irreversible. Consequently, alternative regioselective methods for the reversible formation and breakage of C-O-ether bonds to be performed under mild and sustainable conditions are highly desired. Here we present a biocatalytic shuttle concept making use of corrinoid-dependent methyl transferases from anaerobic bacteria. The two-component enzymatic system consists of a corrinoid protein carrying the cofactor and acting as methyl group shuttle, and a methyltransferase catalyzing both methylation and demethylation in a reversible fashion. Various phenyl methyl ethers are successfully demethylated and serve in addition as sustainable methylating agents for the functionalization of various substituted catechols. Therefore, this methyl transfer approach represents a promising alternative to common chemical protocols and a valuable add-on for the toolbox of available biocatalysts.

Highlights

Established methods for methylation of phenols and demethylation of methyl phenyl ethers rely in general on hazardous reagents or/and harsh reaction conditions and are irreversible
In the first half reaction, methyl transferases (MTases) I binds the substrate and mediates both ether cleavage and transfer of the methyl group onto CoI of the super-reduced cofactor bound to the corrinoid protein (CP)
It relies on the use of just one methyltransferase being the only biocatalyst together with a corrinoid protein (CP) carrying the cobalamin prosthetic group and acting as methyl group shuttle

Summary

Introduction

Established methods for methylation of phenols and demethylation of methyl phenyl ethers rely in general on hazardous reagents or/and harsh reaction conditions and are irreversible. The corrinoid cofactor cycles thereby between the CoIII and the highly reactive CoI state[43] and functions as methyl group shuttle (Fig. 3a) Nature exploits this methyl transfer mainly for O-demethylation, playing an essential role in the amino acid metabolism of eukaryotes as well as in the energy generation of anaerobic organisms[39,44,45]. Several acetogenic bacteria have been described to utilize methyl phenyl ethers as carbon and energy source, amongst others Acetobacterium dehalogenans[46], Acetobacterium woodii[47], Moorella thermoacetica[48], and Desulfitobacterium hafniense[49,50] These organisms encode a complex O-demethylation machinery constituted of four enzymes (Fig. 3b), mediating a methyl group transfer from a substrate onto tetrahydrofolate (FH4) via two half-reactions. To the best of our knowledge, such a system has not previously been investigated for synthetic biocatalytic applications and may represent an alternative to SAM-dependent enzymes as well as related chemical protocols

Methods

Results

Conclusion