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Analysis of the segmental stability of helical peptides by isotope‐edited infrared spectroscopy
Author(s) -
Venyaminov S. Yu.,
Hedstrom J.F.,
Prendergast F.G.
Publication year - 2001
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.1126
Subject(s) - infrared spectroscopy , infrared , spectroscopy , stable isotope ratio , isotope , chemistry , materials science , analytical chemistry (journal) , crystallography , nuclear magnetic resonance , chromatography , physics , optics , nuclear physics , organic chemistry , quantum mechanics
Isotope‐edited infrared spectroscopy has the ability to probe the segmental properties of long biopolymers. In this work, we have compared the infrared spectra of a model helical peptide ( 12 C) Ac‐W‐(E‐A‐A‐A‐R) 6 ‐A‐NH 2 , described originally by Merutka et al. (Biochemistry 1991;30:4245–4248) and three derivatives that are 13 C labeled at the backbone carbonyl of alanines. The locations of six isotopically labeled alanines are at the N‐terminal, C‐terminal, and the middle two repeating units of the peptide. Variation in temperature from 1° to 91°C transformed the peptides from predominantly helical to predominantly disordered state. Amplitude and position of the infrared amide I′ absorption bands from 12 C‐ and 13 C‐labeled segments provided information about the helical content. Temperature dependence of infrared spectra was used to estimate segmental stability. As a control measure of overall peptide stability and helicity (independent of labeling), the temperature dependence of circular dichroism spectra in the far‐UV range at identical conditions (temperature and solvent) as infrared spectra was measured. The results indicate that the central quarter of the 32 amino acids helix has the maximal helicity and stability. The midpoint of the melting curve of the central quarter of the helix is 5.4 ± 0.8°C higher than that of the termini. The N‐terminal third of the helix is more helical and is 2.0 ± 1.4°C more stable than the C‐terminus. Proteins 2001;45:81–89. © 2001 Wiley‐Liss, Inc.