1LZ4: ENTHALPIC DESTABILIZATION OF A MUTANT HUMAN LYSOZYME LACKING A DISULFIDE BRIDGE BETWEEN CYSTEINE-77 AND CYSTEINE-95

Citation:
Abstract
To understand the role of disulfide bridges in protein stability, the thermodynamic changes in the denaturation of two mutant human lysozymes lacking a disulfide bridge between Cys-77 and Cys-95 (C77A and C77/95A) were analyzed using differential scanning calorimetry (DSC). At pH 3.0 and 57 degrees C, the stabilities of both the C77A and C77/95A mutants were decreased about 4.6 kcal.mol-1 in Gibbs free energy change. Under the same conditions, the enthalpy changes (delta H) were 94.8 and 90.8 kcal.mol-1, respectively, which were smaller than that of the wild type (100.8 kcal.mol-1). The destabilization of the mutants was caused by enthalpic factors. Although X-ray crystallography indicated that the mutants preserve the wild-type tertiary structure, removal of the disulfide bridge increased the flexibility of the native state of the mutants. This was indicated both by an increase in the crystallographic thermal factors (B-factors) and by a decrease in the affinity of N-acetylglucosamine trimer [(NAG)3] observed using isothermal titration calorimetry (DTC) due to entropic effects. Thus, the effect of cross-linking on the stability of a protein is not solely explained by the entropy change in denaturation.
PDB ID: 1LZ4Download
MMDB ID: 56805
PDB Deposition Date: 1993/2/3
Updated in MMDB: 2017/12
Experimental Method:
x-ray diffraction
Resolution: 1.8  Å
Source Organism:
Similar Structures:
Biological Unit for 1LZ4: monomeric; determined by author
Molecular Components in 1LZ4
Label Count Molecule
Protein (1 molecule)
1
Human Lysozyme(Gene symbol: LYZ)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

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