Article,

Molecular Dynamics Simulation of Halogen Bonding Mimics Experimental Data for Cathepsin L Inhibition

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Journal of Computer-Aided Molecular Design, 29 (1): 37-46 (2015)
DOI: 10.1007/s10822-014-9802-7

Abstract

A MD simulation protocol was developed to model halogen bonding in protein-ligand complexes by inclusion of a charged extra point to represent the anisotropic distribution of charge on the halogen atom. This protocol was then used to simulate the interactions of cathepsin L with a series of halogenated and non-halogenated inhibitors. Our results show that chloro, bromo and iodo derivatives have progressively narrower distributions of calculated geometries, which reflects the order of affinity I > Br > Cl, in agreement with the IC50 values. Graphs for the Cl, Br and I analogs show stable interactions between the halogen atom and the Gly61 carbonyl oxygen of the enzyme. The halogen-oxygen distance is close to or less than the sum of the van der Waals radii; the C-X center dot center dot center dot O angle is about 170A degrees; and the X center dot center dot center dot O=C angle approaches 120A degrees, as expected for halogen bond formation. In the case of the iodo-substituted analogs, these effects are enhanced by introduction of a fluorine atom on the inhibitors' halogen-bonding phenyl ring, indicating that the electron withdrawing group enlarges the sigma-hole, resulting in improved halogen bonding properties.

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