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T E Creighton

Publications and source records attributed to T E Creighton.

At least 73 records · Page 4Linked to original sources
PubMed1991

(14-38, 30-51) double-disulphide intermediate in folding of bovine pancreatic trypsin inhibitor: a two-dimensional 1H nuclear magnetic resonance study.

An analogue of the BPTI folding intermediate that contains only the disulphide bonds between Cys14 and Cys38 and between Cys30 and Cys51 has been prepared in Escherichia coli by protein engineering methods. The other two Cys residues of native BPTI (at positions 5 and 55) have been replaced by Ser. Essentially complete proton resonance assignments of the analogue were obtained by employing two-dimensional 1H nuclear magnetic resonance techniques. The intermediate has a more extended conformation in the N-terminal (residues 1 to 7) region and there are other differences in the C-terminal (residues 55 to 58) region. The remainder of the protein is substantially identical to native BPTI. The conformational properties of the analogue can explain several aspects of the kinetic role that the normal (14-38, 30-51) intermediate plays in the folding of BPTI.

Amino Acid Sequence↗
PubMed1991

Two-dimensional 1H nuclear magnetic resonance study of the (5-55) single-disulphide folding intermediate of bovine pancreatic trypsin inhibitor.

An analogue of the bovine pancreatic trypsin inhibitor (BPTI) folding intermediate that contains only the disulphide bond between Cys5 and Cys55 has been prepared in Escherichia coli by protein engineering methods, with the other four Cys residues replaced by Ser. Two-dimensional 1H nuclear magnetic resonance studies of the analogue have resulted in essentially complete resonance assignments of the folded form of the protein. The folded protein has a compact conformation that is structurally very similar to that of native BPTI, although there are subtle differences and the folded conformation is not very stable. Approximately half of the protein molecules are unfolded at 3 degrees C, and this proportion increases at higher temperatures. The folded and unfolded conformations are in slow exchange. The conformational properties of the analogue can explain many aspects of the kinetic role that the normal (5-55) intermediate plays in the folding of BPTI.

Amino Acid Sequence↗
PubMed1991

The molten globule protein conformation probed by disulphide bonds.

The molten globule is a compact protein conformation that has a secondary structure content like that of the native protein, but poorly defined tertiary structure. It is a stable state for a few proteins under particular conditions and could be a ubiquitous kinetic intermediate in protein folding. The extent to which native interactions, above the level of the secondary structure, are preserved in this conformation is not so far known. Here we report that alpha-lactalbumin can adopt a molten globule conformation when one of its four disulphide bonds is reduced. In this state, the three other disulphide bonds rearrange spontaneously, at the same rate as when the protein is fully unfolded, to a number of different disulphide bond isomers that tend to maintain the molten globule conformation. That the molten globule state is compatible with a variety of disulphide bond pairings suggests that it is unlikely to be stabilized by many specific tertiary interactions.

Animals↗
PubMed1991

The 5-55 single-disulphide intermediate in folding of bovine pancreatic trypsin inhibitor.

An analogue of the BPT1 folding intermediate that contains only the disulphide bond between Cys-5 and Cys-55 has been prepared by mutation of the other four Cys residues to Ser. On the basis of its circular dichroism and 1H-nuclear magnetic resonance spectra and its electrophoretic mobility, this intermediate is shown to be at least partially folded at low temperatures. This probably accounts for several of the unique properties of this intermediate observed during folding.

Animals↗
PubMed1990

Protein folding.

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Chemical Phenomena↗
PubMed1990

Folding proteins.

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Aprotinin↗
PubMed1989

Effect of protein conformation on rate of deamidation: ribonuclease A.

The effect of the folded conformation of a protein on the rate of deamidation of a specific asparaginyl residue has been determined. Native and unfolded ribonuclease A (RNase A) could be compared under identical conditions, because stable unfolded protein was generated by breaking irreversibly the protein disulfide bonds. Deamidation of the labile Asn-67 residue of RNase A was followed electrophoretically and chromatographically. At 80 degrees C, similar rates of deamidation were observed for the disulfide-bonded form, which is thermally unfolded, and the reduced form. At 37 degrees C and pH 8, however, the rate of deamidation of native RNase A was negligible, and was more than 30-fold slower than that of reduced, unfolded RNase A. This demonstrates that the Asn-67 residue is located in a local conformation in the native protein that greatly inhibits deamidation. This conformation is the beta-turn of residues 66-68.

Amines↗
PubMed1988

Further experimental studies of the disulfide folding transition of ribonuclease A.

Two very different mechanisms of folding have been proposed from experimental studies of disulfide formation in reduced ribonuclease A. (1) A pathway in which the rate-limiting step separates fully folded protein from all other disulfide intermediates and occurs solely in three-disulfide intermediates. (2) A multiple pathway mechanism with different rate-limiting steps for each pathway. The various rate-limiting steps involve disulfide breakage, formation, and rearrangement in intermediates with one, two, three, and four protein disulfides. To distinguish between these two mechanisms, we have carried out further studies of both unfolding and refolding. Refolding of reduced ribonuclease A requires three-disulfide intermediates to accumulate; negligible refolding occurs when only the nearly random one- and two-disulfide intermediate species are populated. Therefore, no rate-limiting steps of the type postulated in mechanism (2) occur in intermediates with one and two protein disulfides. Unfolding and disulfide reduction is an all-or-none process; no disulfide intermediates accumulate to detectable levels or precede the rate-limiting step. Mechanism (2) requires that such intermediates precede the rate-limiting step and accumulate to substantial levels. The different proposals were shown not to result from the use of different solution conditions or disulfide reagents; the two sets of data are not inconsistent. Instead, the inappropriate mechanism (2) resulted from an incorrect kinetic analysis and misinterpretation of the kinetics of disulfide formation and breakage.

Cystine↗
PubMed1988

On the relevance of non-random polypeptide conformations for protein folding.

The possibility that any non-random conformation in reduced bovine pancreatic trypsin inhibitor (BPTI) and ribonuclease A might be significant for folding has been considered, using the experimental data available on forming the first disulphide bond in each. It is a thermodynamic necessity that whatever conformation stabilises a particular disulphide bond be stabilised to the same extent by the presence of the disulphide. The stabilising effects of disulphides are known approximately, so the stability of any non-random conformation found in a one-disulphide intermediate can be estimated in the absence of the disulphide bond. The non-random conformation in the BPTI intermediates is sufficiently labile to indicate that it would be expected to be present in no more than 5% of the reduced BPTI molecules. There is much less non-random conformation apparent in ribonuclease A. Whatever conformations are represented in the bulk of these two reduced proteins cannot favour disulphide formation and further productive folding.

Aprotinin↗
PubMed1988

Toward a better understanding of protein folding pathways.

Experimental observations of how unfolded proteins refold to their native three-dimensional structures contrast with many popular theories of protein folding mechanisms. The available experimental evidence (ignoring slow cis-trans peptide bond isomerization) is largely consistent with the following general scheme: under folding conditions, unfolded protein molecules rapidly equilibrate between different conformations prior to complete refolding. This rapid prefolding equilibrium favors certain compact conformations that have somewhat lower free energies than the other unfolded conformations. Some of the favored conformations are important for productive folding. The rate-limiting step occurs late in the pathway and involves a high-energy, distorted form of the native conformation; there appears to be a single transition state through which essentially all molecules refold. Consequently, proteins are not assembled via a large number of independent pathways, nor is folding initiated by a nucleation event in the unfolded protein followed by rapid growth of the folded structure. The known folding pathways involving disulfide bond formation follow the same general principles. An exceptional folding mechanism for reduced ribonuclease A proposed by Scheraga et al. (Scheraga, H.A., Konishi, Y., Rothwarf, D.M. & Mui, P.W. (1987) Proc. Natl. Acad. Sci. USA 84, 5740-5744) is shown to result from experimental shortcomings, an incorrect kinetic analysis, and a failure to consider the kinetics of unfolding.

Aprotinin↗
PubMed1987

Conformations of intermediates in the folding of the pancreatic trypsin inhibitor.

Intermediates in the folding pathway of the bovine pancreatic trypsin inhibitor (PTI) have been examined by 1H nuclear magnetic resonance (n.m.r.). The intermediates were trapped during the reoxidation and consequent refolding of reduced PTI by alkylating free thiols; each intermediate contained different disulphide linkages. The n.m.r. spectra reveal that conformational features of the native protein are present in the intermediate containing just one of the three normal disulphide linkages (30-51). As additional normal disulphide bonds are formed, the conformation becomes more similar to that of the native protein. Introduction of additional but incorrect disulphide bonds does not lead to an increase in observable globular structure. A description of the folding process in terms of the conformations of the different intermediates is proposed. The significance of these results for the general mechanism of protein folding is outlined.

Amino Acid Sequence↗
PubMed1987

Sequences of the genes and polypeptide precursors for two bovine protease inhibitors.

The genes for bovine pancreatic trypsin inhibitor and a homologous protease inhibitor have been characterized using messenger RNA, clones of complementary DNA copies and genomic fragments. Both genes consist of three exons and two introns and are virtually identical in sequence, suggesting that recently they either arose by gene duplication or were subject to gene conversion. However, they differ markedly in their promoter regions and in a segment within the first intron. Perhaps as a consequence, the two genes can be expressed using different transcription start sites, and the two proteins are found in different bovine tissues. Each middle exon encodes primarily the mature protein, while the other two exons define amino- and carboxyl-terminal extensions of 33 or 35 and 7 amino acid residues, respectively. The amino-terminal extensions contain a signal peptide-like sequence, suggesting that the proteins are destined for cellular compartments. The remaining extensions at both ends may be involved in targetting of the proteins, and there are some similarities to other proteins destined for cellular compartments.

Amino Acid Sequence↗