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Regioselectivity Inversion of an O‐Methyltransferase via Semi‐rational Mutagenesis Combined with Metal Ion Substitution

S‐adenosyl‐L‐methionine (SAM)‐dependent O‐methyltransferases (O‐MTs) are a class of valuable and attractive biocatalysts for alkylation of catechols. In this work, an O‐methyltransferase (GeOMT) from the plant Galanthus elwesii was identified and characterised. GeOMT methylated a series of catechols with excellent regioselectivity. Moreover, a strategy was developed that combines structure‐directed protein engineering and metal ion substitution for regioselective inversion of GeOMT. The resultant W50M/A53N/Y186K triple variant preferentially coordinated Ni2+ instead of Mg2+ and displayed almost complete inversion in regioselectivity from 1 : 99 to 94 : 6 (para/meta) for 4‐nitrocatechol, the para‐methylated product of which is a vital plant growth regulator. This represents a promising strategy for regioselectivity improvement of O‐MTs.