Previato JO, Vinogradov E, Silva MAE, Oliveira PAV, Fonseca LM, et al.
Carbohydrate research •
Glucuronoxylomannogalactans (GXMGals) are characteristic capsular polysaccharides produced by the opportunistic fungus C. neoformans, which are implicated in cryptococcal virulence, via impairment of the host immune response. We determined for the first time the structure of a lipoglucuronomannogalactan (LGMGal), isolated from the surface of a mutant C. neoformans carrying a deletion in the UDP-GlcA decarboxylase gene. Monosaccharide composition and methylation analyses, as well as nuclear magnetic resonance spectroscopy were employed in discerning the structure. Our results show that the polysaccharide structure of the LGMGal differs from GXMGal by the absence of xylose and 2-O-acetylated mannose residues. LGMGal consists of a galactan main chain -[-6-α-Gal-]-, where every second Gal residue is substituted at O-3 with an oligosaccharide α-Man6OAc-3-α-Man-4-(β-GlcA-3)-β-Gal-; components in italic being non-stoichiometric. The substitution rate of β-Galp units by GlcpA is 35%. Additionally, we determined that the glycolipid anchor of the LGMGal is based on an myo-inositol phosphoceramide composed of C-phytosphingosine and monohydroxylated lignoceric acid (2OHC fatty acid).
Phosphatidylserine (PS) and surface carbohydrates (SC) are known as virulence factors that may contribute to the different clinical symptoms ranging from self-healing cutaneous leishmaniasis lesions to fatal visceral disease. Leishmania (Viannia) braziliensis causes localized cutaneous leishmaniasis (LCL) and mucocutaneous leishmaniasis (MCL). We analyzed PS exposure and SC expression associated with 2 primary L. braziliensis isolates from patients with LCL or MCL. The role of PS exposure was also addressed during promastigotes phagocytosis by macrophages. We observed higher PS exposure on the surface of late stationary growth phase promastigotes from patients with LCL, compared with those from patients with MCL, and both strains were alive during PS display. Reduction in the infectivity index was observed during macrophage interaction with late stationary growth phase promastigotes in which PS was blocked by annexin V. The major surface carbohydrates detected on LCL and MCL promastigotes were α-Man, α-Glc, and α-Gal. However, α-β-GalNAc, although observed on the surface of the LCL strain during the late stationary growth phase was highly expressed on the surface of early stationary growth phase promastigotes. Our results suggest that PS and SC can modulate interactions between Leishmania organisms and host cells and may be important for the outcome of the clinical course of diseases caused by L. braziliensis.
