Extremely fast hydrogen exchange of ribonuclease-(1-118) as compared with native RNase A and its implication for the conformational energy state.
RNase-(1-118) containing native disulfide bonds is similar in fold to native RNase A but not of lowest Gibbs energy as compared with the isomers containing non-native disulfide bonds. The present n.m.r. studies have indicated a dramatic increase in the exchange rate of all of the 'protected' amide protons of RNase-(1-118) over RNase A. A calculation shows a large increase in the rate of 'opening' of the structure. The exchange rate of the protected amide protons of RNase-(1-120) is slower than RNase-(1-118) but much faster than RNase A. Binding with a synthetic complementing fragment (114-124) markedly reduces the exchange rate of 20 to 25 amide protons of RNase-(1-118). It has previously been shown that binding with a complementing fragment of RNase-(1-118) generates a lowest Gibbs energy state. Thus, using available thermodynamic information for interpretation, we suggest that a) removal of six carboxy terminal residues of RNase A would disrupt coupling between these residues and those distant in the structure (loss of extra stabilizing energy), b) this would, in turn, alter the enthalpy-entropy compensation in such a way that the magnitude of Gibbs energy change favoring folding is significantly reduced without a large change of fold and c) in this activated state the molecule would be highly motile.
Roy
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S
Dibello
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Taniuchi
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H
D004220:Disulfides; D006860:Hydrogen Bonding; D007700:Kinetics; D010446:Peptide Fragments / Q000378:metabolism*; D011487:Protein Conformation; D012259:Ribonuclease, Pancreatic / Q000378:metabolism*
D004220:Disulfides; D010446:Peptide Fragments; D012259:Ribonuclease, Pancreatic