Molecular cloning, cell localization and binding affinity to DNA replication proteins of the p36/LACK protective antigen from Leishmania infantum

The p36/LACK antigen from Leishmania, an analogue of the receptor for activated protein kinase C (PKC), induces high levels of protection against parasite infection in the BALB/c mouse model. This protection is more than twice as high as that elicited by major parasite antigens such as soluble Leishmania antigen or the main surface protease gp63. We have cloned and purified p36/LACK from Leishmania infantum, the causative agent of visceral leishmaniasis in Europe. This protein belongs to the large family of WD 40 repeat proteins confined to eukaryotes and involved in numerous regulatory functions. Differential solubilization and immunofluorescence experiments indicate that p36/LACK is present close to the kinetoplast disc in the cell cytoplasm, probably bound to multiprotein complexes but not to membrane structures. These complexes probably also include cytoplasm PKC isoforms. The use of a genetically-encoded peptide library indicates that p36/LACK binds sequences present in several proteins involved in DNA replication and RNA synthesis. The recognition and binding sequences present in vacuolar proteins and at the beta-chain of major histocompatability complex (MHC) class II suggest the involvement of this regulatory protein in the early mechanisms triggering the protective immune response of the host against the parasite infection.