title: Structure of a mutant of tyrosyl-tRNA synthetase with enhanced catalytic properties.
abstract: One surprising outcome of applying the techniques of protein engineering to the enzyme tyrosyl-transfer RNA synthetase was that the enzyme's activity could actually be increased by a specific sequence change. In particular, altering residue threonine 51 to a proline (mutant TP51) increased the enzyme's affinity for tyrosyl adenylate complexes. The non-additive effect of combining the TP51 mutation with a second sequence alteration (histidine 48 to a glycine) suggested that the effect of the TP51 change might be mediated by a structural change involving the peptide backbone. To address the question of the mechanism by which the TP51 change increases the activity of tyrosyl-tRNA synthetase we have determined the structure of the mutant enzyme. We find the change has a purely local effect on the structure of the enzyme, and conclude that the increased activity of the TP51 mutant probably results from the replacement of the polar threonine residue by a non-polar group: in the wild-type enzyme substrate binding is disfavoured by the displacement of solvent from the vicinity of threonine 51. This unfavourable effect is absent in the TP51 mutant.
mesh_terms: D000249:Adenosine Monophosphate; D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D002384:Catalysis; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D006639:Histidine; D009154:Mutation; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D013912:Threonine; D014443:Tyrosine; D014448:Tyrosine-tRNA Ligase / Q000235:genetics / Q000378:metabolism*
chemical_list: D013912:Threonine; D000249:Adenosine Monophosphate; D014443:Tyrosine; D006639:Histidine; D000604:Amino Acyl-tRNA Synthetases; D014448:Tyrosine-tRNA Ligase