Researchers at Keio University, Japan, have inverted an enzyme's enantioselectivity despite not knowing its structure or reaction mechanism.

The enzyme, arylmalonate decarboxylase, catalyses the decarboxylation of ?-aryl-?-malonate into (R)-?-arylpropionate. The team suspected that a cysteine residue at position 188 in the enzyme acts as a proton donor during the reaction. If so, enantioselectivity should be reversible by changing its position.

The key question was where to move it to? Homology screening against other enzymes with similar reaction mechanisms pointed to the amino acid at position 74 as vital in controlling optical yields. To test this, cysteine 188 was mutated to glycine and glycine 74 to cysteine. Dramatically, this led to a complete conversion of the product to the S-configuration with an increase in enantiomeric excess.

This may pave the way towards allowing the specificity of other potentially useful biocatalysts to be altered based on their reaction mechanisms. Chris Incles