Leishmania RAB7: characterisation of terminal endocytic stages in an intracellular parasite

Area of Science:

• * Molecular Parasitology
• * Cell Biology
• * Immunology

Background:

• * Leishmania parasites reside within host macrophages, utilizing the endo-membrane system to evade immune clearance.
• * Intracellular Leishmania amastigotes possess high proteolytic/lysosomal activity, potentially degrading MHC class II molecules and disrupting antigen presentation.
• * Characterizing endosomal-lysosomal events is crucial for understanding Leishmania immune evasion strategies.

Purpose of the Study:

• * To characterize a Leishmania homologue of Rab7, a known late endosomal marker.
• * To investigate the role of Leishmania Rab7 in the parasite's interaction with the host endo-membrane network.
• * To elucidate the involvement of endosomal-lysosomal pathways in Leishmania pathogenesis.

Main Methods:

• * Expression and purification of recombinant Leishmania major Rab7 (LmRAB7) protein.
• * GTP binding assays for LmRAB7.
• * Antibody generation and immunolocalization studies.
• * Immunoelectron microscopy of axenic Leishmania mexicana amastigotes.

Main Results:

• * Leishmania major Rab7 (LmRAB7) is expressed throughout the parasite's life cycle.
• * LmRAB7 shares homology with Trypanosoma cruzi and Trypanosoma brucei Rab7 proteins but possesses a kinetoplastid-specific insertion.
• * Recombinant LmRAB7 binds GTP.
• * Antibodies against LmRAB7 recognize structures between the nucleus and kinetoplast.
• * Immunoelectron microscopy confirmed Leishmania mexicana Rab7 (LmexRAB7) localization in late endosomes/lysosomes, overlapping with the cysteine proteinase B marker.

Conclusions:

• * Leishmania Rab7 is a functional homologue of mammalian Rab7, localizing to the late endosomal/lysosomal pathway.
• * This characterization provides insights into the endosomal trafficking mechanisms employed by Leishmania.
• * Understanding LmRAB7 function can reveal novel targets for anti-Leishmania therapies.