Mechanism of falcipain-2 inhibition by a,b-unsaturated benzo[1,4]diazepin-2-one methyl ester

Falcipain-2 (FP-2) is a papain-family cysteine
protease of Plasmodium falciparum whose primary function
is to degrade the host red cell hemoglobin, within the
food vacuole, in order to provide free amino acids for
parasite protein synthesis. Additionally it promotes host
cell rupture by cleaving the skeletal proteins of the erythrocyte
membrane. Therefore, the inhibition of FP-2 represents
a promising target in the search of novel anti-malarial
drugs. A potent FP-2 inhibitor, characterized by the presence
in its structure of the 1,4-benzodiazepine scaffold and
an a,b-unsaturated methyl ester moiety capable to react
with the Cys42 thiol group located in the active site of
FP-2, has been recently reported in literature. In order to
study in depth the inhibition mechanism triggered by this
interesting compound, we carried out, through ONIOM
hybrid calculations, a computational investigation of the
processes occurring when the inhibitor targets the enzyme
and eventually leads to an irreversible covalent Michael
adduct. Each step of the reaction mechanism has been accurately characterized and a detailed description of each
possible intermediate and transition state along the pathway
has been reported.