Cell Biology

Ancient Protein Sorting

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Science  21 Feb 2003:
Vol. 299, Issue 5610, pp. 1153
DOI: 10.1126/science.299.5610.1153c

The protozoan parasite Giardia intestinalis is a representative of a family of ancient eukaryotes. The parasite multiplies within the intestine and in order to propagate further must produce an infectious encysted form that can resist the external environment. During cyst formation, the parasite produces cyst wall proteins that are synthesized in the endoplasmic reticulum and are sorted to specialized secretory vesicles, the encystation-specific vesicles. Marti et al. examined the protein sorting mechanisms employed by the parasite. During encystation, cells package proteins destined for the cyst wall and variant-specific surface proteins separately. The parasites lack an easily identifiable Golgi complex—the secretory sorting organelle used to package regulated secretory granules in higher eukaryotic cells. Instead, Giardia appears to sort secretory proteins earlier in the secretory pathway, immediately after exit from the endoplasmic reticulum, so that the encystation-specific vesicles themselves subserve some of the functions that in higher eukaryotes are performed by the Golgi complex. — SMH

MBC in Press 10.1091/mbc.E02-05-0467 (2003).

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