From Natural Methylation to Versatile Alkylations Using Halide Methyltransferases

Halide methyltransferases (HMTs) enable the enzymatic synthesis of S‐adenosyl‐l‐methionine (SAM) from S‐adenosyl‐l‐homocysteine (SAH) and methyl iodide. Characterisation of a range of naturally occurring HMTs and subsequent protein engineering led to HMT variants capable of synthesising ethyl, propyl, and allyl analogues of SAM. Notably, HMTs do not depend on chemical synthesis of methionine analogues, as required by methionine adenosyltransferases (MATs). However, at the moment MATs have a much broader substrate scope than the HMTs. Herein we provide an overview of the discovery and engineering of promiscuous HMTs and how these strategies will pave the way towards a toolbox of HMT variants for versatile chemo‐ and regioselective biocatalytic alkylations. Naturally occurring and engineered promiscuous halide methyltransferases (HMTs) enable S‐adenosyl‐l‐methionine analogues to be enzymatically synthesised and recycled, using simple and readily available alkyl iodides as alkyl donors. In combination with promiscuous methyltransferases (MTs), they dramatically expand the bioalkylation toolbox.