Size heterogeneity among antigenically related Giardia lamblia variant-specific surface proteins is due to differences in tandem repeat copy number

Abstract

Giardia lamblia undergoes antigenic variation by modulating the expression of the different genes that comprise the trophozoite's variant-specific surface protein (VSP) repertoire. We studied an epitope that is conserved among VSPs expressed by cloned trophozoite lines derived from the independent G. lamblia isolates WB, G3M, Be-2, and CAT. The epitope recognized by monoclonal antibody 6E7 lies entirely within the region of tandemly repeated 65-amino-acid units that is characteristic of these size-variant VSPs. Northern (RNA) hybridization, cDNA cloning, and DNA sequence analysis indicate that size heterogeneity among these VSPs is due to differences in the number of repetitive units.on August 4, 2020 by guest http://iai.asm.org/ Downloaded from

A New Gene Family ( ariel ) Encodes Asparagine-Rich Entamoeba histolytica Antigens, Which Resemble the Amebic Vaccine Candidate Serine-Rich E. histolytica Protein

“…(iii) At least four ariel genes are constitutively expressed, so antigenic diversity may exist within a single parasite isolate rather than between separate parasite isolates (as is the case for SREHP and amebic chitinase) (4,22). It is unclear whether amebae have any variably expressed antigens, such as the var proteins of P. falciparum, the variable surface proteins of Giardia lamblia, and the variable surface glycoproteins of Trypanosoma brucei (3,18,27).…”

A novel palmitoyl acyl transferase controls surface protein palmitoylation and cytotoxicity in Giardia lamblia

“…VSPs are proteins with frequent CXXC motifs and are transported through the ER by their signal peptides (McCaffery and Gillin, 1994). To date, all known VSPs are membrane proteins that contain similar 25‐amino acid transmembrane domain and a highly conserved CRGKA cytoplasmic tail (Mowatt et al ., 1994). This conserved C‐terminus may function as a membrane‐anchoring domain (Papanastasiou et al ., 1996) or as a sorting motif to the plasma membrane (Marti et al ., 2003a).…”

Regulation of Antigenic Variation inGiardia lamblia

“…Antigenic variation in Giardia involves variantspecific surface proteins (VSPs) (86). VSPs are key players in Giardia antigenic variation and are the focus of great controversy in the field because their characteristics may be related to regulation of the switching process (29).…”

“…It was later demonstrated that all vsp genes are transcribed but that all but one are silenced by an RNA interference (RNAi)-like mechanism. This mRNA always corresponds to the variant expressed on the parasite surface (5,85,86). After VSP switching occurs, the original transcript disappears with the appearance of a distinct VSP mRNA (3, 85,144,147).…”