Structural determinants of Ca2+ binding sites within proteins typically comprise several acidic residues in appropriate juxtaposition. Three residues (Ala-83, Gln-86, and Ala-92) in human lysozyme are characteristically mutated to Lys, Asp, and Asp, ...
Structural determinants of Ca2+ binding sites within proteins typically comprise several acidic residues in appropriate juxtaposition. Three residues (Ala-83, Gln-86, and Ala-92) in human lysozyme are characteristically mutated to Lys, Asp, and Asp, respectively, in natural Ca2+ binding lysozymes and alpha-lactalbumins. The effects of these mutations on the stability and Ca2+ binding properties of human lysozyme were investigated using calorimetry and were interpreted with crystal structures. The double mutant, in which Glu-86 and Ala-92 were replaced with Asp, clearly showed Ca2+ binding affinity, whereas neither point mutant showed Ca2+ affinity, indicating that both residues are essential. The further mutation of Ala-83 --> Lys did not affect the Ca2+ binding of the double mutant. The point mutations Ala-83 --> Lys and Glu-86 --> Asp did not affect the stability, whereas the mutation Ala-92 --> Asp was about 1.3 kcal/mol less stable. Structural analyses showed that both Asp-86 and Lys-83 were exposed to solvent. Side chains of Asp-86 and Asp-91 were rotated in opposite directions about chi1 angle, as if to reduce the electrostatic repulsion. The charged amino acids at the Ca2+ binding site did not significantly affect stability of the protein, possibly because of the local conformational change of the side chains.
Related Citations:
Thermodynamic changes in the binding of Ca2+ to a mutant human lysozyme (D86/92). Enthalpy-entropy compensation observed upon Ca2+ binding to proteins. Kuroki, R., Nitta, K., Yutani, K. (1992) J Biol Chem 267: 24297
Entropic Stabilization of a Mutant Human Lysozyme Induced by Calcium Binding Kuroki, R., Kawakita, S., Nakamura, H., Yutani, K. (1992) Proc Natl Acad Sci U S A 89: 6803
Crystal Structure of the Apo- and Holomutant Human Lysozymes with an Introduced Ca2+ Binding Site Inaka, K., Kuroki, R., Kikuchi, M., Matsushima, M. (1991) J Biol Chem 266: 20666
Design and Creation of a Ca2+ Binding Site in Human Lysozyme to Enhance Structural Stability Kuroki, R., Taniyam, Y., Seko, C., Nakamura, H., Kikuchi, M., Ikehara, M. (1989) Proc Natl Acad Sci U S A 86: 6903
Organizational Affiliation:
Central Laboratories for Key Technology, Kirin Brewery Co. Ltd., 1-13-5 Fukuura, Kanazawa-ku, Yokohama 236 Japan. r-kuroki@kirin.co.jp
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