Analysis of electrostatic interactions and their relationship to conformation and stability of bovine pancreatic trypsin inhibitor

The modified Tanford-Kirkwood electrostatic theory has been employed to evaluate pK values for all charge sites in the bovine pancreatic trypsin inhibitor (BPTI). 13C NMR titration data were obtained for all titrating groups except arginine residues in BPTI at nearly constant ionic strength in 0.1 M...

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Bibliographic Details
Published in:Biochemistry (Easton) 1982-01, Vol.21 (21), p.5241-5251
Main Authors: March, Keith L, Maskalick, David G, England, Richard D, Friend, Stephen H, Gurd, Frank R. N
Format: Article
Language:English
Subjects:
Animals
Cattle
Chemical Phenomena
Chemistry, Physical
conformational analysis
electrical properties
Hydrogen-Ion Concentration
Magnetic Resonance Spectroscopy
mathematical models
Mathematics
Models, Chemical
Protein Conformation
trypsin inhibitor (pancreatic)
Trypsin Inhibitor, Kazal Pancreatic
Trypsin Inhibitors
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Summary:The modified Tanford-Kirkwood electrostatic theory has been employed to evaluate pK values for all charge sites in the bovine pancreatic trypsin inhibitor (BPTI). 13C NMR titration data were obtained for all titrating groups except arginine residues in BPTI at nearly constant ionic strength in 0.1 M NaCl, at 41 degrees C. The chemical shifts of 46 resonances were found to be sensitive to pH. The pK values of these titrating resonances compared well with those computed by the modified Tanford-Kirkwood electrostatic theory. A conformational change involving the NH2- and COOH-terminal and nearby residues is shown to be partly electrostatically driven by the formation of a salt bridge between the alpha-amino and alpha-carboxyl groups at mid-pH values. The computed total electrostatic free energy of the molecule is found to be stabilizing at neutral pH despite the substantial net positive charge borne by the protein under such conditions.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00264a020