Designer enzymes

Natural enzymes are constructed from a pool of 20 genetically encoded amino acids, and enzymes typically require one or more additional small organic molecules or metal ions to function. In addition, amino acids can be added to enzymes after protein translation, and these noncanonical amino acids (NCA) can extend the catalytic repertoire of the original enzymes. Using a chemical mutagenesis strategy, Claire Windle et al. (pp. 2610–2615) incorporated 13 different NCA side chains at 12 different positions within the active site of a Staphylococcus aureus N-acetylneuraminic acid lyase to alter its function. The authors found that a modified N-acetylneuraminic acid lyase with a 2,3-dihydroxypropyl cysteine (Dpc) residue at position 190 had increased activity for the aldol reaction of erythrose with pyruvate, compared with a wild-type enzyme. Analysis of enzyme kinetics revealed that the altered substrate specificity of the Dpc-modified enzyme could not be replicated by inserting any of the 20 genetically encoded amino acids at position 190. Structural and modeling studies revealed that the shape and functionality of the Dpc side chain remodeled the active site to enable a change in substrate specificity. According to the authors, improved methods for enzyme redesign and the availability of a variety of NCA side chains could facilitate the engineering of enzymes with catalytic functions not found in nature. - Read at PNAS