trans

LEISHMANIA 231
(1,6)myo-inositol-1-PO 4 -lipid motif, the hallmark
of all GPI anchors. LPPG differs from
the Leishmania GIPLs by the presence of the
phosphoceramide moiety, a feature found
in the LPPG of Acanthamoeba castellanii and
in a lipid anchor found in Dictyostelium
discoideum. Moreover T. cruzi LPPG contains
2-aminoethylphosphonate as does the
Acanthamoeba castellanii phosphoglycan.
LEISHMANIA
Leishmania exist as flagellated, extracellular
promastigotes in the midgut of their sand fly
vector, and as intracellular, aflagellar amastigotes
in the phagolysosomes of the mammalian
macrophage. The parasites are transmitted
when a sand fly takes a blood meal from an
infected individual. Within the sand fly midgut
the promastigotes develop from the avirulent
procyclic form to the virulent metacyclic
form in a process termed metacyclogenesis.
Throughout their life cycle, Leishmania survive
and proliferate in highly hostile environments
and have evolved special mechanisms
which enable them to endure these adverse
conditions, including a dense cell surface glycocalyx
composed of lipophosphoglycan,
glycosylinositolphospholipids and secreted
glycoconjugates, proteophosphoglycan (PPG)
and secreted acid phosphatase (sAP).
Lipophosphoglycan
Lipophosphoglycan (LPG), the predominant
cell surface glycoconjugate of Leishmania
promastigotes, is localized over the entire parasite
surface including the flagellum. Found in
all species of Leishmania that infect humans,
sAP
LPG
PG
Cap
Repeating unit
GIPLs
GPI-anchored
proteins
PPG
-Ser-PO 4 -
Core
FIGURE 10.3 Schematic representation of the surface coat and secreted glycoconjugates of Leishmania. The small
oval ‘repeat unit’ represents Gal-Man-PO 4 units. In PPG and sAP, the repeat unit chain is attached to the polypeptide
via Man-PO 4 -serine linkage. GIPLs, glycosylinositolphospholipids; LPG, lipophosphoglycan; PG, phosphoglycan;
PPG, proteophosphoglycan; sAP, secreted acid phosphatase.
BIOCHEMISTRY AND CELL BIOLOGY: PROTOZOA