Structural Studies by ¹H NMR and Molecular Modeling of Peptide Substrates of Thermolysin in Relation with its Proteasic Activity in Water and Glycerol

Abstract

In an attempt to explain the relationship between conformations of peptide substrates of thermolysin in natural form and the experimental enzymatic cleavages, five peptides of various length were studied in two solvents H₂O and glycerol, which may mimic the catalytic environmental conditions. As NMR failed to define sufficently rough constraints to ensure a convergence of a refinement process for such short and flexible peptides, the conformational space was first searched using the MCMM method. The generated structures were then clustered in families using a 0.3Å rmsd criterion and the derived structural characteristics were compared to the experimental NMR parameters. In a first approach, the NMR consistent conformations were compared with the structure of a thermolysin bound peptidic inhibitor ZG^PLL to characterize the free-ligand predisposition to be cleaved. Further molecular dynamic calculations were performed at 300 K on the conformations corresponding to families in agreement with the ZG^PLL structure in order to obtain information on their stability and on the trajectories of the torsion angles involved in the active site recognition. In conclusion, for four studied peptides, some conformations were found to be in agreement with 5 of the 8 cleavages experimentally observed.