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Amino Acids with Hydrogen‐Bonding Side Chains have an Intrinsic Tendency to Sample Various Turn Conformations in Aqueous Solution
Journal article

Amino Acids with Hydrogen‐Bonding Side Chains have an Intrinsic Tendency to Sample Various Turn Conformations in Aqueous Solution

Andrew Hagarman, Daniel Mathieu, Siobhan Toal, Thomas J Measey, Harald Schwalbe and Reinhard Schweitzer‐Stenner
Chemistry : a European journal, v 17(24), pp 6789-6797
06 Jun 2011
PMID: 21547966

Abstract

vibrational spectroscopy conformational distributions unfolded state NMR spectroscopy intrinsic propensities
Local structure in unfolded proteins, especially turn segments, has been suggested to initiate the hierarchical protein‐folding process. To determine the intrinsic propensity to form such turn structures, amide I′ band profiles of the Raman, IR, and vibrational circular dichroism (VCD) spectra, and several structure‐sensitive NMR J‐coupling constants, have been measured for a series of GxG (x=D, N, T, C) peptides, in which the central x residues are abundant in various turn motifs in folded proteins. In addition, we revisited earlier measured GSG experimental data. To check whether this relatively high propensity for these residues to sample turns reflects an intrinsic propensity, the experimental data were analyzed in terms of conformational distributions that can be described as a superposition of two‐dimensional Gaussian distributions associated with different so‐called mesostates. The analysis reveals that the investigated residues sample dihedral angles similar to those found in the corner residues of various turns, namely, type I/I′, II/II′, and IV β‐turns. Aspartic acid (D) was found to predominantly sample regions attributed to turns, including distributions at the upper border of the upper‐right quadrant of the Ramachandran plot, which bear some resemblance to asx‐turns observed in proteins. This conformation enables hydrogen bonding between the side‐chain carboxylate and the C‐terminal amide group. Altogether, the study shows that the high propensity for T, S, C, N, and D to be located in turn motifs reflects, to a substantial degree, an intrinsic property and supports the role of these residues as initiation sites for hierarchical folding processes that can lead to compact structures in the unfolded state of peptides and proteins. Know when to fold: The intrinsic propensity of amino acids to adopt elements of secondary structure is vital in the absence of long‐range interactions in the earliest stages of protein folding. Polar residues were demonstrated to have an intrinsic tendency to adopt dihedral angles found predominantly in turn motifs (see figure). These results demonstrate that the high occurrence of polar residues in turns reflects an intrinsic property.

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Web of Science research areas
Chemistry, Multidisciplinary
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