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Chloride‐ion concentration dependence of molecular dimension in the acid‐denatured state of equine β‐lactoglobulin
Author(s) -
Yamada Yoshiteru,
Yajima Takeo,
Tsukamoto Seiichi,
Nakagawa Kanako,
Fujiwara Kazuo,
Kihara Hiroshi,
Ikeguchi Masamichi
Publication year - 2007
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889807008278
Subject(s) - globular protein , chemistry , chloride , guanidinium chloride , ion , crystallography , native state , organic chemistry , enzyme
The chloride‐ion concentration dependence of the molecular dimension in the acid‐denatured state of equine β‐lactoglobulin (ELG) was investigated by small‐angle X‐ray scattering. In the presence of chloride ion, ELG has a globular and compact conformation (the A state). The molecular dimension of ELG increases little with decreasing chloride‐ion concentration. A remarkable dependence was observed for a mutant protein in which both Cys66 and Cys160 were replaced with Ala (C66A/C160A). In the presence of chloride ion, C66A/C160A has a globular and compact conformation, like the wild type. In the absence of chloride ion, however, the molecular dimension and shape was close to that in the urea‐unfolded state. Previously, we have shown that the helix content in the acid‐denatured state increases with decreasing chloride‐ion concentration [Yamada et al. (2006). Proteins Struct. Funct. Bioinf. 63 , 595–602]. These results suggest that the secondary structure in the A state is mainly determined by non‐local interactions. When they are absent in an expanded conformation, the local interactions become predominant and the amount of non‐native α‐helix increases.