Malaria remains one of the most important infectious diseases in the world. Plasmodial cysteine proteases are proposed to be promising targets for novel antimalarial drug design. Vivapain-2 and vivapain-3 are cysteine proteases from Plasmodium vivax and apparent orthologs of falcipain-2 and falcipain-3 from Plasmodium falciparum. Model structures of vivapain-2 and vivapain-3 have been derived using the comparative protein modeling approach and validated by various structure/geometry verification tools. Correlation between the interaction energies calculated based on the docking studies of the inhibitors and the corresponding association constants (k_ass) provide additional validation for the structures. Moreover, some of the biochemical differences observed between the vivapains may be explained by the results of the docking studies. The overall structures of the two vivapains are similar to each other as well as to the falcipains with most of the catalytic residues conserved. At the same time, some important differences are observed between the sizes of the binding pockets as well as some of the residues involved in binding. The study suggests a likelihood of developing common inhibitors for these enzymes provided the interesting differences in the binding pockets of these enzymes are critically considered during such an attempt. The results of the current study can be utilized in de novo drug design for effective treatment of malaria.

Key words: Plasmodium vivax, Cysteine proteases, Vivapain, Comparative protein modeling, Docking.