ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A series of site-directed mutagenesis experiments have been performed in our laboratory, bearing on the Zn2+ metalloprotease from Bacillus stearothermophillus, a protein very closely related to thermolysin (TLN), and their consequences on the binding of inhibitors belonging to the thiolate, carboxylate, hydroxamate, and phosphoramidate classes of compounds [A. Beaumont et al. (1995), J. Biol. Chem., Vol. 270, pp. 16803-16808]. An unexpected result related to the mutation of protonated His231, which resides at the entrance of the enzymatic cavity, into an Ala residue, shown to leave the binding affinities of thiolate inhibitors unaffected, but to abolish almost completely those of the phosphoramidate inhibitors. In order to account for such contrasting differential responses, we have undertaken a theoretical study of the comparative binding affinities of a representative thiol inhibitor, thiorphan (I) and a phosphoramidate (II), to a model of the enzymatic cavity of both the native and the mutated protein, encompassing up to 27 residues. The computations of inter- (ΔE) and intramolecular interactions were done with the sum of interactions between fragments ab initio computed procedure [N. Gresh et al. (1984), Theoret. Chim. Acta. Vol. 66, pp. 1-20; (1985), Theoret. Chim. Acta, Vol. 67, pp. 11-32; (1986), Int. J. Quant. Chem., Vol. 29, pp. 101-118; (1994), in Modelling the Hydrogen Bond, American Chemical Society Symposia, Vol. 569, D. A. Smith, Ed., American Chemical Society, pp. 82-112; N. Gresh (1995), J. Comput. Chem., Vol. 16, 856-882]. The energy balances for the His231 → Ala mutation incorporate a solvation energy contribution, computed using the Langlet et al. Continuum procedure [J. Langlet et al. (1988), J. Phys. Chem., Vol. 92, pp. 1617-1631], and this term was shown to play a decisive role in the comparative energy balances of the thiolate vs phosphoramidate inhibitors. Whereas the resolvation energy was able to compensate for the loss of ΔE induced by the H231 A mutation for the complex of I, thus accounting for its insensitivity to the mutation, such a compensation did not occur in the case of II, leading in its complexes to an overall loss of about 7 kcal/mole in the mutated cavity with respect to the native one. These results emphasized the critical role played by solvation in enzyme-inhibitor recognition processses. © 1997 John Wiley & Sons, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
Permalink
