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Involvement of disulfide bonds and histidine 172 in a unique β‐sheet to α‐helix transition of α 1 ‐acid glycoprotein at the biomembrane interface
Author(s) -
Nishi Koji,
Komine Yoshio,
Fukunaga Naoko,
Maruyama Toru,
Suenaga Ayaka,
Otagiri Masaki
Publication year - 2006
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.20923
Subject(s) - chemistry , helix (gastropod) , histidine , collagen helix , glycoprotein , folding (dsp implementation) , protein structure , biochemistry , stereochemistry , amino acid , biophysics , triple helix , biology , ecology , snail , electrical engineering , engineering
Abstract Human α 1 ‐acid glycoprotein (AGP), which is comprised of 183 amino acid residues and 5 carbohydrate chains, is a major plasma protein that binds to basic and neutral drugs as well as to steroid hormones. It has a β‐sheet–rich structure in aqueous solution. Our previous findings suggest that AGP forms an α‐helix structure through an interaction with biomembranes. We report herein on a study of the mechanism of α‐helix formation in AGP using various modified AGPs. The disulfide reduced AGP (R‐AGP) was extensively unfolded, whereas asialylated AGP (A‐AGP) maintained the native structure. Intriguingly, reduced and asialylated AGP (RA‐AGP) increased the α‐helix content as observed in the presence of biomembrane models, and showed a significant decrease in ligand binding capacity. This suggests that AGP has an innate tendency to form an α‐helix structure, and disulfide bonds are a key factor in the conformational transition between the β‐sheet and α‐helix structures. However, RA‐AGP with all histidine residues chemically modified (HRA‐AGP) was found to lose the intrinsic ability to form an α‐helix structure. Furthermore, disulfide reduction of the H172A mutant expressed in Pichia pastoris also caused a similar loss of folding ability. The present results indicate that disulfide bonds and the C‐terminal region, including H172 of AGP, play important roles in α‐helix formation in the interaction of the protein with biomembranes. Proteins 2006. © 2006 Wiley‐Liss, Inc.