Comparing helix stability in proteins and peptides : the alpha-helix of Ribonuclease T1 /
An investigation of the determinants of helix stability has
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739667861&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | An investigation of the determinants of helix stability has been undertaken using Ribonuclease T1 as a model system. Ribonuclease T1 features a single []-helix spanning residues 13 through 29. A mutation was made in the protein, glycine 23 to alanine, which allowed a peptide of residues 13 through 29 to show significant helix formation in aqueous solution. Substitutions were made in this peptide and in the intact protein at position 21 to measure the helix propensities of the commonly-occurring amino acids. The measured propensities for most of the amino acids showed excellent agreemnent between peptide and protein. Among the exceptions are: proline, which produced a non-folding protein; asparagine and aspartic acid, which showed unusually high stability in the protein; histidine, which showed unusual instability in the peptide. Helix propensities measured in the ribonuclease T1 peptide/protein were compared with those measured in other systems. Reasonable agreement was found between all the systems except two. It was found that alanine-based peptides over-estimate the propensity differences by a factor of two, and that host/guest experiments under-estimate them by a factor of two to three. The helical content of the peptides was also measured in two concentrations of trifluoroethanol (TFE). The helix propensities of the amino acids increase nonuniformly in TFE. This is in agreement with recent observations in alanine-based peptides, and suggests that hydration plays a role in determining helix propensity. To investigate the role of side-chain interactions, four peptides were synthesized which had mutations of charged residues at the C- terminus of the helix. These mutants have been made in the intact protein by others. The peptides showed that helix stability was increased at neutral pH by removing unfavorable charge/helix macrodipole interactions at the C-terminus, in agreement with the results found in the protein. The change in []G of helix formation of two of the variant peptides is in excellent agreement with [][]G's reported for the intact protein. |
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| Item Description: | Vita. "Major Subject: Biochemistry". In title, numerals, symbols, and subscripts are used. Alpha appears as symbol on physical piece. |
| Physical Description: | xii, 119 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 104-118. |