Drug development against Leishmania donovani, the pathogen that causes visceral 
leishmaniasis in humans, is currently an active area of research given the 
widespread prevalence of the disease and the emergence of resistant strains. The 
immunosuppressive drug cyclosporin is known to have antiparasitic activity 
against a variety of pathogens. The receptor for cyclosporin is the protein 
cyclophilin, which is a ubiquitous peptidylprolyl isomerase. The crystal 
structure of cyclophilin from L. donovani complexed with cyclosporin has been 
solved at 2.6 A resolution. The thermodynamic parameters of the interaction have 
been determined using spectroscopic and calorimetric techniques. A detailed 
effort has been made to predict the thermodynamic parameters of binding from 
computations based on the three-dimensional crystal structure. These results 
were in good agreement with the corresponding experimental values. Furthermore, 
the structural and biophysical results have been discussed in the context of 
leishmanial drug resistance and could also set the stage for the design of 
potent non-immunosuppressive antileishmanials.