Jd. Bangs et al., EXPRESSION OF BLOOD-STREAM VARIANT SURFACE GLYCOPROTEINS IN PROCYCLICSTAGE TRYPANOSOMA-BRUCEI - ROLE OF GPI ANCHORS IN SECRETION, EMBO journal, 16(14), 1997, pp. 4285-4294
Using transformed procyclic trypanosomes, the synthesis, intracellular
transport and secretion of wildtype and mutant variant surface glycop
rotein (VSG) is characterized. We find no impediment to the expression
of this bloodstream stage protein in insect stage cells, VSG receives
a procyclic-type phosphatidylinositol-specific phospholipase C-resist
ant glycosyl phosphatidylinositol (GPI) anchor, dimerizes and is N-gly
cosylated. It is transported to the plasma membrane with rapid kinetic
s (t(1/2) similar to 1 h) and then released by a cell surface zinc-dep
endent metalloendoprotease activity, a possible homolog of leishmanial
gp63. Deletion of the C-terminal GPI addition signal generates a solu
ble form of VSG that is exported with greatly reduced kinetics (t(1/2)
similar to 5 h). Fusion of the procyclic acidic repetitive protein (P
ARP) GPI anchor signal to the C-terminus of the truncated VSG reporter
restores both GPI addition and transport competence, suggesting that
GPI anchors play a critical role in the folding and/or forward transpo
rt of newly synthesized VSG, The VSG-PARP fusion is also processed nea
r the C-terminus by events that do not involve N-linked oligosaccharid
es and which are consistent with GPI side chain modification, This une
xpected result suggests that GPI processing may be influenced by adjac
ent peptide sequence or conformation.