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  • Biochemistry and Biotechnology  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Comparison of CD spectra in the aromatic region on a series on variant proteins substituted at a unique position of tryptophan synthase α-subunit (1989)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 5 (1989), S. 211-217 
    Details
    ISSN: 0887-3585
    Keywords: tyrosin ; mutant protein ; amino acid substitution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: CD spectra in the aromatic region of a series of the mutant α-subunits of tryptophan synthase from Escherichia coli, substituted at position 49 buried in the interior of the molecule, were measured at pH 7.0 and 25°C. The measurements were taken to gain information on conformational change produced by single amino acid substitutions. The CD spectra of the mutant proteins, substituted by Tyr or Trp residue in place of Glu residue at position 49, showed more intense positive bands due to one additional Tyr or Trp residue at position 49. The CD spectra of other mutant proteins also differed from that of the wild-type protein, despite the fact that the substituted residues at position 49 were not aromatic. Using the spectrum of the wild-type protein (Glu49) as a standard, the spectra of the other mutants were classified into three major groups. For 10 mutant proteins substituted by Ile, Ala, Leu, Met, Val, Cys, Pro, Ser, His, or Gly, their CD values of bands (due to Tyr residues) decreased in comparison with those of thewild-type protein. The mutant protein substituted by Phe also belonged to this group. These substituted amino acid residues are more hydrophobic than the original residue, Glu. In the second group, three mutant proteins were substituted by Lys, Gln, or Asn, and the CD values of tyrosyl bands increased compared to those of the wild-type proteins. These residues are polar. In the third group, the CDvalues of tyrosyl bands of two mutant proteins substituted by Asp or Thr were similar to those of the wild-type protein, except for oneband at 276.5 nm. these results suggested that the changes in the CD spectra for the mutant proteins were affected by the hydrophobicity of the residuesat position 49.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340050304
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Role of conserved proline residues in stabilizing tryptophan synthase α subunit: Analysis by mutants with alanine or glycine (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 90-98 
    Details
    ISSN: 0887-3585
    Keywords: calorimetry ; unfolding of protein ; CD spectra ; denaturation by guanidine hydrochloride ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: To study the role of Pro residues in the conformation and conformational stability of a protein, nine mutant α subunits of tryptophan synthase from Escherichia coli, in which Ala or Gly was substituted for each of six Pro residues (positions 28, 57, 62, 96, 132, and 207) that are conserved in 10 microoganisms, were constructed by means of site-directed mutagenesis. The far-ultraviolet (UV) CD spectra of five mutant α subunits with Ala in place of Pro were identical to the spectrum of the wild-type protein, the exception being the mutant at position 207 (P207A). CD values in the far-UV region were less negative for P207A, indicating that the Pro residue at position 207 plays a role in maintaining the intact structure of the α subunit. The negative CD values of the Gly mutants examined (P28G, P96G, and P132G) were also decreased. Calorimetric measurements showed that the two mutants at position 28 (P28G and P28A) gave two peaks in the excess heat capacity curve, whereas the wild type and other Pro mutants had only a single peak. The stability of each mutant protein relative to that of the wild type was about the same for P57A, less for P62A and P132A, and markedly decreased for P96A and P207A, which are substituted at less mobile positions. The changes of denaturation entropy (ΔΔdS) at the denaturation temperature of the wild-type protein (54.1 °C at pH 9.0) were positive for P57A, P62A, and P132A, but negative for P96A, P207A, and P132G. The present results do not indicate that the differences in stability (ΔdG) among Pro substitutions are caused only by an entropic factor, as might be theoretically expected. The decreases in stability for P96A and P207 were due to the considerable decrease in denaturation enthalpy, although they were partly compensated for by the decrease in entropy. Our results also suggest that Pro-28 stabilizes the interaction between two domains of the α subunit.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090203
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    Paper (German National Licenses)
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