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Proline Isomerism Leads to Multiple Folded Conformations of Calbindin D9k: Direct Evidence from Two-Dimensional 1H NMR Spectroscopy
Walter J. Chazin, Johan Kördel, Torbjörn Drakenberg, Eva Thulin, Peter Brodin, Thomas Grundström and Sture Forsén
Proceedings of the National Academy of Sciences of the United States of America
Vol. 86, No. 7 (Apr. 1, 1989), pp. 2195-2198
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/33444
Page Count: 4
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A complete analysis of calbindin D9k by two-dimensional 1H nuclear magnetic resonance spectroscopy has established the existence of two conformations for the folded protein in solution. Well-resolved major and minor resonances in a ratio of 3:1 are observed throughout the 1H NMR spectrum. Two-dimensional exchange experiments show that the major and minor species are related by an equilibrium process. Analysis of short proton-proton distances along the peptide backbone, identified by two-dimensional nuclear Overhauser effect spectroscopy, provides unambiguous evidence that the two forms of the folded protein differ only in the isomerization state of the peptide bond between Gly-42 and Pro-43. Cis-trans isomerism of Pro-43 is thereby directly identified as the cause of multiple conformations for the folded protein in solution. In addition, when Pro-43 is mutated to a glycine residue there is no indication of multiple conformations. These results provide evidence for the possibility of conformational heterogeneity in the native state of globular proteins.
Proceedings of the National Academy of Sciences of the United States of America © 1989 National Academy of Sciences