Protease-catalyzed hydrolysis of substrate mimetics (inverse substrates): A new approach reveals a new mechanism.

Contrary to common protease substrates, the hydrolysis of 4-guanidinophenyl esters of the Boc-Xaa-OGp type by trypsin and trypsin-like proteases performs easily and independently of the structure and chirality of the acyl moiety. The hydrolysis of this new class of substrate mimetics, previously called inverse substrates, is enabled by the highly specific leaving group. However, the mechanism cannot be explained on the basis of the conventional binding model which defines the interactions between the protease and its substrate. Hydrolysis and aminolysis kinetics, protein-ligand docking, and molecular dynamics studies have been carried out in order to get insight into the catalytic mechanism which holds for these substrate mimetics. The experimental and theoretical results obtained for the serine protease trypsin suggest a novel extended kinetic model. It explains the hydrolysis of these types of protease substrates and accounts for the structural consequences for their aminolysis.