Purification and characterization of selenomethionyl thymidylate synthase from Escherichia coli: comparison with the wild-type enzyme
| Autor: | R. Bruce Dunlap, Jerome D. Odom, Ralph J. Cisneros, Mary S. Weir, Jeffrey O. Boles, J. E. Villafranca |
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| Rok vydání: | 1991 |
| Předmět: |
Specificity constant
Protein Conformation Stereochemistry Auxotrophy Buffers Biology medicine.disease_cause Biochemistry Thymidylate synthase Selenium chemistry.chemical_compound Protein structure X-Ray Diffraction Enzyme Stability Escherichia coli medicine Amino Acid Sequence Amino Acids Selenomethionine chemistry.chemical_classification Binding Sites Methionine Temperature Thymidylate Synthase Hydrogen-Ion Concentration Kinetics Enzyme chemistry Covalent bond biology.protein |
| Zdroj: | Biochemistry. 30:11073-11080 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi00110a009 |
| Popis: | Replacement of methionine (Met) residues by selenomethionine (SeMet) was recently shown to facilitate the crystallographic analysis of protein structure through the application of multi-wavelength anomalous diffraction techniques [Yang et al. (1990) Science (Washington, D.C.) 249, 1398-1405]. The availability of SeMet-containing proteins provides an excellent opportunity to evaluate the effects of the complete replacement of Met by SeMet. We chose to compare the properties of selenomethionyl thymidylate synthase isolated from Escherichia coli DL41 (a methionine auxotroph) and wild-type (wt) enzyme obtained from E. coli Rue10. An improved purification procedure for thymidylate synthase was developed which permitted the isolation of 25 mg of pure protein from 2 g of E. coli in 90% yield in no more than 8 h. The pure wt and SeMet enzymes exhibited specific activities 40% higher than published values. Thermal stability studies at 30 degrees C in degassed buffer showed that the SeMet enzyme (t1/2 67 h) was 8-fold less stable than wt enzyme (t1/2 557 h). The half-lives for the latter enzymes in nondegassed buffers at 30 degrees C were decreased by 2-fold, thus indicating the sensitivity of the enzyme to dissolved oxygen. Both enzymes exhibited essentially the same kinetic and binding properties, including Km(dUMP) (1.2 x 10(-6) M), specificity constant (1.6 x 10(6) s-1 M-1), and Kd for 5-fluorodeoxyuridylate binding (1.2 nM) in covalent inhibitory ternary complexes. In addition, X-ray crystallographic analysis by difference Fourier synthesis showed there was no significant difference in conformation between the SeMet enzyme and the wt enzyme. |
| Databáze: | OpenAIRE |
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