1EQ4

CRYSTAL STRUCTURES OF SALT BRIDGE MUTANTS OF HUMAN LYSOZYME

1EQ4 の概要

• エントリーDOI: 10.2210/pdb1eq4/pdb
• 関連するPDBエントリー: 1C43 1EQ5 1EQE
• 分子名称: LYSOZYME, SODIUM ION (3 entities in total)
• 機能のキーワード: salt bridge, stability, hydrolase
• 由来する生物種: Homo sapiens (human)
• 細胞内の位置: Secreted: P61626
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 14742.70

構造登録者

Takano, K.,Tsuchimori, K.,Yamagata, Y.,Yutani, K. (登録日: 2000-04-03, 公開日: 2000-04-19, 最終更新日: 2024-11-20)

主引用文献

Takano, K.,Tsuchimori, K.,Yamagata, Y.,Yutani, K.
Contribution of salt bridges near the surface of a protein to the conformational stability.
Biochemistry, 39:12375-12381, 2000

PubMed Abstract: Salt bridges play important roles in the conformational stability of proteins. However, the effect of a surface salt bridge on the stability remains controversial even today; some reports have shown little contribution of a surface salt bridge to stability, whereas others have shown a favorable contribution. In this study, to elucidate the net contribution of a surface salt bridge to the conformational stability of a protein, systematic mutant human lysozymes, containing one Glu to Gln (E7Q) and five Asp to Asn mutations (D18N, D49N, D67N, D102N, and D120N) at residues where a salt bridge is formed near the surface in the wild-type structure, were examined. The thermodynamic parameters for denaturation between pH 2.0 and 4.8 were determined by use of a differential scanning calorimeter, and the crystal structures were analyzed by X-ray crystallography. The denaturation Gibbs energy (DeltaG) of all mutant proteins was lower than that of the wild-type protein at pH 4, whereas there was little difference between them near pH 2. This is caused by the fact that the Glu and Asp residues are ionized at pH 4 but protonated at pH 2, indicating a favorable contribution of salt bridges to the wild-type structure at pH 4. Each contribution was not equivalent, but we found that the contributions correlate with the solvent inaccessibility of the salt bridges; the salt bridge contribution was small when 100% accessible, while it was about 9 kJ/mol if 100% inaccessible. This conclusion indicates how to reconcile a number of conflicting reports about role of surface salt bridges in protein stability. Furthermore, the effect of salts on surface salt bridges was also examined. In the presence of 0.2 M KCl, the stability at pH 4 decreased, and the differences in stability between the wild-type and mutant proteins were smaller than those in the absence of salts, indicating the compensation to the contribution of salt bridges with salts. Salt bridges with more than 50% accessibility did not contribute to the stability in the presence of 0.2 M KCl.

PubMed: 11015217
DOI: 10.1021/bi000849s

実験手法

X-RAY DIFFRACTION (1.8 Å)