RESUMO
The protozoan parasite, Leishmania donovani, undergoes several molecular adaptations and secretes many effector molecules for host cell manipulation and successful parasitism. The current study identifies an albumin-like secretory protein, expressed in its extracellular promastigote forms. A leishmanial complementary DNA sequence of a partial gene has been cloned, and the encoded peptide (14 kD) is used for the production of polyclonal antibody. This targeted antibody identifies a large native protein (66.421 kD), expressed stage-specifically in promastigotes. Through electron microscopic studies, the native protein is found to be localized in the flagellar pocket and flagella and at the surface of the promastigotes. This native protein is purified with the same customized antibody for future characterization and sequencing. The sequence analysis reveals its homology with the mammalian serum albumin. It is evidenced from in silico studies that this albumin-like protein remains associated with long-chain fatty acids while in vitro studies indicate its close association with membrane cholesterol. Since antibody-mediated blocking compromises the parasite infectivity, these leishmanial albumin-like molecules are hereby proposed to play an instrumental role in the infectivity of L. donovani to peripheral blood monocyte cells. Thus, identification and characterization of an albumin-like protein in L. donovani promastigotes may be interpreted as a molecular adaptation candidate. It may be hypothesized that the parasite mimics the mammalian system for importing fatty acids into the intracellular amastigotes, facilitating its host cell infectivity.