Sc. Ilgoutz et al., Glycosylphosphatidylinositol biosynthetic enzymes are localized to a stable tubular subcompartment of the endoplasmic reticulum in Leishmania mexicana, EMBO J, 18(13), 1999, pp. 3643-3654
Glycosylphosphatidylinositols (GPI) are essential components in the plasma
membrane of the protozoan parasite Leishmania mexicana, both as membrane an
chors for the major surface macromolecules and as the sole class of free gl
ycolipids. We provide evidence that L.mexicann dolichol-phosphate-mannose s
ynthase (DPMS), a key enzyme in GPI biosynthesis, is localized to a distinc
t tubular subdomain of the endoplasmic reticulum (ER), based on the localiz
ation of a green fluorescent protein (GFP)-DPMS chimera and subcellular fra
ctionation experiments. This tubular membrane (termed the DPMS tubule) is a
lso enriched in other enzymes involved in GPI biosynthesis, can be specific
ally stained with the fluorescent lipid, BODIPY-C-5-ceramide, and appears t
o be connected to specific subpellicular microtubules that underlie the pla
sma membrane. Perturbation of microtubules and DPMS tubule structure in viv
o results in the selective accumulation of GPI anchor precursors, but not f
ree GPIs. The DPMS tubule is closely associated morphologically with the si
ngle Golgi apparatus in non-dividing and dividing cells, appears to exclude
luminal ER resident proteins and is labeled, together with the Golgi appar
atus, with another GFP chimera containing the heterologous human Golgi mark
er pl,beta 1,2-N-acetylglucosaminyltransferase-I. The possibility that the
DPMS-tubule is a stable transitional ER is discussed.