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T P Graycar

Publications and source records attributed to T P Graycar.

6 recordsLinked to original sources
PubMed1994

Packing selection of Bacillus lentus subtilisin and a site-specific variant.

The crystallization of a variant of Bacillus lentus subtilisin and the native enzyme was achieved using identical conditions. The variant B. lentus was found to grow in two crystal forms, form 1 and form 2, whereas the native B. lentus subtilisin enzyme crystallized in only one, form 1. Form 2 crystals, once obtained, were found to grow much more rapidly than form 1 crystals. The lattice contacts and structural changes giving both crystal forms have been examined. The results show that crystal form 2 has a more complex network of interactions. There is also a small surface conformational change in the form 2 structure relative to the native and variant form 1 crystals and at least two solvent molecules bound to the enzyme in crystal form 1 are displaced in crystal form 2. In addition, a site specific substitution in the variant at position 27 induces a 'short' lattice contact which does not exist in the native B. lentus or the form 2 variant B. lentus. These results suggest that in some circumstances engineered variants could be designed to crystallize more rapidly than the native enzyme.

Journal Article↗
PubMed1987

Recruitment of substrate-specificity properties from one enzyme into a related one by protein engineering.

The Bacillus licheniformis and Bacillus amyloliquefaciens subtilisins differ by 31% in protein sequence and by factors of greater than 60 in catalytic efficiency, kcat/Km, toward various substrates. Despite large differences in sequence and substrate specificity for these serine proteases, only two amino acid substitutions (residues 156 and 217) occur within 4 A (contact distance) of modeled substrates, and a third substitution (residue 169) is within 7 A. The three B. licheniformis substitutions (Ser-156/Ala-169/Leu-217) were introduced into the wild-type B. amyloliquefaciens subtilisin (Glu-156/Gly-169/Tyr-217) by site-directed mutagenesis. The substrate specificity of the triple mutant approaches that of B. licheniformis enzyme when assayed with seven different substrates that vary in charge, size, and hydrophobicity. Thus, specificity properties of distantly related and functionally divergent enzymes can be exchanged by limited amino acid replacements, in this case representing less than 4% of the sequence differences.

Amino Acids↗
PubMed1987

Designing substrate specificity by protein engineering of electrostatic interactions.

Protein engineering of electrostatic interactions between charged substrates and complementary charged amino acids, at two different sites in the substrate binding cleft of the protease subtilisin BPN', increases kcat/Km toward complementary charged substrates (up to 1900 times) and decreases kcat/Km toward similarly charged substrates. From kinetic analysis of 16 mutants of subtilisin and the wild type, the average free energies for enzyme-substrate ion-pair interactions at the two different sites are calculated to be -1.8 +/- 0.5 and -2.3 +/- 0.6 kcal/mol (1 cal = 4.18 J) [at 25 degrees C in 0.1 M Tris X HCl (pH 8.6)]. The combined electrostatic effects are roughly additive. These studies demonstrate the feasibility for rational design of charged ligand binding sites in proteins by tailoring of electrostatic interactions.

Binding Sites↗
PubMed1985

Engineering an enzyme by site-directed mutagenesis to be resistant to chemical oxidation.

Site-directed mutagenesis can be employed to alter activity critical residues in proteins which are susceptible to chemical oxidation. Previous studies have implicated methionine 222 as a primary site for oxidative inactivation of subtilisin (Stauffer, C. E., and Etson, D. (1969) J. Biol. Chem. 244, 5333-5338). Because of uncertainties in predicting which amino acid would be the optimal substitute for methionine 222, we prepared all 19 amino acid substitutions at this site in the cloned subtilisin gene using a cassette mutagenesis method (Wells, J. A., Vasser, M., and Powers, D. P. (1985) Gene (Amst.), in press). Mutant enzymes were expressed in Bacillus subtilis and were found to vary widely in specific activity. Mutants containing nonoxidizable amino acids (i.e. Ser, Ala, and Leu) were resistant to inactivation by 1 M H2O2, whereas methionine and cysteine enzymes were rapidly inactivated. These studies demonstrate the feasibility of improving oxidative stability in proteins by site-directed mutagenesis.

Amino Acids↗