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Position dependence of amino acid intrinsic helical propensities II: Non-charged polar residues: Ser, Thr, Asn, and Gln

Published online by Cambridge University Press:  01 October 1999

MICHAEL PETUKHOV
Affiliation:
European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, Heidelberg D-69012, Germany
KOICHI UEGAKI
Affiliation:
Osaka National Research Institute, AIST, Ikeda, Osaka 563, Japan
NOBORU YUMOTO
Affiliation:
Osaka National Research Institute, AIST, Ikeda, Osaka 563, Japan
SUSUMU YOSHIKAWA
Affiliation:
Osaka National Research Institute, AIST, Ikeda, Osaka 563, Japan
LUIS SERRANO
Affiliation:
European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, Heidelberg D-69012, Germany
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Abstract

The assumption that the intrinsic α-helical propensities of the amino acids are position independent was critical in several helix/coil transition theories. In the first paper of these series, we reported that this is not the case for Gly and nonpolar aliphatic amino acids (Val, Leu, Met, and Ile). Here we have analyzed the helical intrinsic propensities of noncharged polar residues (Ser, Thr, Asn, and Gln) at different positions of a model polyalanine-based peptide. We found that Thr is more favorable (by ∼0.3 kcal/mol) at positions N1 and N2 than in the helix center, although for Ser, Asn, and Gln the differences are smaller (±0.2 kcal/mol), and in many cases within the experimental error. There is a reasonable agreement (±0.2 kcal/mol) between the calculated free energies, using the ECEPP/2 force field equipped with a hydration potential, and the experimental data, except at position N1.

Type
Research Article
Copyright
© 1999 The Protein Society

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