1coa
From Proteopedia
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THE EFFECT OF CAVITY CREATING MUTATIONS IN THE HYDROPHOBIC CORE OF CHYMOTRYPSIN INHIBITOR 2
Overview
Hydrophobic residues in the core of a truncated form of chymotrypsin, inhibitor 2 (CI2) have been mutated in order to measure their contribution, to the stability of the protein. The free energy of unfolding of wild-type, and mutants was measured by both guanidinium chloride-induced denaturation, and differential scanning calorimetry. The two methods give results for, the changes in free energy on mutation that agree to within 1% or 2%. The, average change in the free energy of unfolding (+/- standard deviation), for an Ile-->Val mutation is 1.2 +/- 0.1 kcal mol-1, for a Val-->Ala, mutation 3.4 +/- 1.5 kcal mol-1, and for either an Ile-->Ala or a, Leu-->Ala mutation 3.6 +/- 0.6 kcal mol-1. This gives an average change in, the free energy of unfolding for deleting one methylene group of 1.3 +/-, 0.5 kcal mol-1. Two significant correlations were found between the change, in the free energy of unfolding between wild-type and mutant, delta delta, GU-F, and the environment of the mutated residue in the protein. The first, is between delta delta GU-F and the difference in side-chain, solvent-accessible area buried between wild-type and mutant (correlation, coefficient = 0.81, 10 points). The second and slightly better correlation, was found between delta delta GU-F and N, the number of methyl/methylene, groups within a 6-A radius of the hydrophobic group deleted (correlation, coefficient = 0.84, 10 points). The latter correlation is very similar to, that found previously for barnase, suggesting that this relationship is, general and applies to the hydrophobic cores of other globular proteins., The combined data for C12 and barnase clearly show a better correlation, with N (correlation coefficient = 0.87, 30 points) than with the change in, the solvent-accessible surface area (correlation coefficient = 0.82, 30, points). This indicates that the packing density around a particular, residue is important in determining the contribution the residue makes to, protein stability. In one case, Ile-->Val76, a mutation which deletes the, C delta 1 methyl group of a buried side chain, a surprising result was, obtained. This mutant was found to be more stable than wild-type by 0.2, +/- 0.1 kcal mol-1. We have solved and analyzed the crystal structure of, this mutant and find that there are small movements of side chains in the, core, the largest of which, 0.7 A, is a movement of the side chain that, has been mutated.(ABSTRACT TRUNCATED AT 400 WORDS)
About this Structure
1COA is a Single protein structure of sequence from Hordeum vulgare. Full crystallographic information is available from OCA.
Reference
Effect of cavity-creating mutations in the hydrophobic core of chymotrypsin inhibitor 2., Jackson SE, Moracci M, elMasry N, Johnson CM, Fersht AR, Biochemistry. 1993 Oct 26;32(42):11259-69. PMID:8218191
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