A pleiotropic response to the calpain inhibitor MDL28170 was detected in the tomato parasite
Phytomonas serpens.
Ultrastructural studies revealed that MDL28170 caused mitochondrial swelling, shortening of flagellum and disruption
of trans Golgi network. This effect was correlated to the inhibition in processing of cruzipain-like molecules, which presented
an increase in expression paralleled by decreased proteolytic activity. Concomitantly, a calcium-dependent cysteine
peptidase was detected in the parasite extract, the activity of which was repressed by pre-incubation of parasites with
MDL28170. Flow cytometry and Western blotting analyses revealed the differential expression of calpain-like proteins
(CALPs) in response to the pre-incubation of parasites with the MDL28170, and confocal fluorescence microscopy confirmed
their surface location. The interaction of promastigotes with explanted salivary glands of the insect
Oncopeltus fasciatus
was reduced when parasites were pre-treated with MDL28170, which was correlated to reduced levels of surface
cruzipain-like and gp63-like molecules. Treatment of parasites with anti-
Drosophila melanogaster
(Dm) calpain antibody
also decreased the adhesion process. Additionally, parasites recovered from the interaction process presented higher
levels of surface cruzipain-like and gp63-like molecules, with similar levels of CALPs cross-reactive to anti-Dm-calpain
antibody. The results confirm the importance of exploring the use of calpain inhibitors in studying parasites’ physiology.
