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Observation of the closing of individual hydrogen bonds during TFE–induced helix formation in a peptide
Author(s) -
Jaravine Victor A.,
Alexandrescu Andrei T.,
Grzesiek Stephan
Publication year - 2001
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.48501
Subject(s) - hydrogen bond , chemistry , intramolecular force , crystallography , helix (gastropod) , peptide bond , peptide , stereochemistry , population , residue (chemistry) , molecule , organic chemistry , ecology , biochemistry , snail , biology , demography , sociology
Helix formation of an S‐peptide analog, comprising the first 20 residues of Ribonuclease A and two additional N‐terminal residues, was studied by measuring hydrogen bond (H‐bond) h3 J NC′ scalar couplings as a function of 2,2,2‐trifluoroethanol (TFE) concentration. The h3 J NC′ couplings give direct evidence for the closing of individual backbone N‐H•••O = C H‐bonds during the TFE‐induced formation of secondary structure. Whereas no h3 J NC′ correlations could be detected without TFE, α‐helical (i,i +4) H‐bond correlations were observed for the amides of residues A5 to M15 in the presence of TFE. The analysis of individual coupling constants indicates that α‐helix formation starts at the center of the S‐peptide around residue E11 and proceeds gradually from there to both peptide ends as the TFE concentration is increased. At 60% to 90% TFE, well‐formed α‐helical H‐bonds were observed for the amides hydrogens of residues K9 to Q13, whereas H‐bonds of residues T5 to A8, H14, and M15 are affected by fraying. No intramolecular backbone H‐bonds are present at and beyond the putative helix stop signal D16. As the h3 J NC′ constants represent ensemble averages and the dependence of h3 J NC′ on H‐bond lengths is very steep, the size of the individual h3 J NC′ coupling constants can be used as a measure for the population of a closed H‐bond. These individual populations are in agreement with results derived from the Lifson‐Roig theory for coil‐to‐helix transitions. The present work shows that the closing of individual H‐bonds during TFE‐induced helix formation can be monitored by changes in the size of H‐bond scalar couplings.