First published online November 23, 2005
Journal of Cell Science 118, 2304e (2005)
© The Company of Biologists Limited
GPI anchors away
Glycosyl-phosphatidyinositol (GPI) anchors allow a wide variety of proteins to attach to membranes and may also affect their trafficking. In African trypanosomes - the cause of sleeping sickness - the variant surface glycoproteins (VSGs) that allow these protozoa to evade host immune responses have two GPI anchors. The transferrin receptor present in the flagellar pocket, by contrast, has only one, and most proteins lack them. Jay Bangs and co-workers have therefore examined the roles of GPI valence in determining the fate of trypanosome proteins by comparing endo- and exo-cytic trafficking of native proteins with and without anchors (see p. 5499). They show that, whereas (GPI)2 proteins are stably expressed at the cell surface and (GPI)0 proteins are degraded in lysosomes, (GPI)1 proteins appear at the cell surface, in the external medium, at the flagellar pocket and in lysosomes - the fraction present at each location depends on the protein. The authors propose that this is because the (GPI)1 proteins cycle though the flagellar pocket and endosomes until they are released into the medium or undergo lysosomal degradation - other aspects of the protein structure could determine the relative efficiency of each step. The presence of two GPI anchors on VSGs may enable them to avoid this fate and remain at the cell surface.
Related articles in JCS:
- GPI valence and the fate of secretory membrane proteins in African trypanosomes
- Kevin J. Schwartz, Ronald F. Peck, Ngii N. Tazeh, and James D. Bangs
JCS 2005 118: 5499-5511.
[Abstract]
[Full Text]
