1i22
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MUTANT HUMAN LYSOZYME (A83K/Q86D/A92D)
OverviewOverview
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.
DiseaseDisease
Known diseases associated with this structure: Amyloidosis, renal OMIM:[153450], Microphthalmia, syndromic 1 OMIM:[309800]
About this StructureAbout this Structure
1I22 is a Single protein structure of sequence from Homo sapiens with as ligand. Active as Lysozyme, with EC number 3.2.1.17 Full crystallographic information is available from OCA.
ReferenceReference
Structural and thermodynamic responses of mutations at a Ca2+ binding site engineered into human lysozyme., Kuroki R, Yutani K, J Biol Chem. 1998 Dec 18;273(51):34310-5. PMID:9852096
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