The construction of mutations in the active site of the tyrosyl tRNA
synthetase from Bacillus stearothermophilus has allowed us to deduce the
relative impörtance of the substrate contacts to transition state binding.
The feature dominating the energetics is the exchange reaction with water
molecules: thus by deleting a poor H-bonding contact to the substrate we
could increase the affinity of the enzyme for substrate. Furthermore by
straining the polypeptide backbone by introducing a proline residue, we
could improve the interaction of a histidine residue with the substrate.
Thus enzymes affinities can be bettered by protein engineering in vitro
