A new gene family (ariel) encodes asparagine-rich Entamoeba histolytica antigens, which resemble the amebic vaccine candidate serine-rich E. histolytica protein

Abstract

A family of genes, called ariel, are named for and encode asparagine-rich Entamoeba histolytica antigens containing 2 to 16 octapeptide repeats. Ariel proteins, which are constitutively expressed by trophozoites, belong to a large antigen family that includes the serine-rich E. histolytica protein (SREHP), an amebic vaccine candidate.

FIG. 1

Alignment of amino acids, in single letter code, of eight predicted E. histolytica Ariel proteins (Ariel-1 to Ariel-8) with those of SREHP and SREDP. Because the Ariel proteins differ only in the number and sequence of the octapeptide repeats (shaded boxes), single amino- and carboxy-terminal Ariel sequences are shown. Sequences identical to Ariel-1 are marked with dashes, gaps are marked with dots, and COOH-terminal stop codons are marked with asterisks. Arrows indicate the locations of primers used for PCR and RACE. Tetrapeptide and octapeptide repeats of SREHP and SREDP are marked with unshaded boxes. Ariel-1, Ariel-2, Ariel-4, and Ariel-5 are derived from a cDNA library or RACE, while Ariel-2, Ariel-3, Ariel-6, Ariel-7, and Ariel-8 are derived from a gDNA library or PCR products.

FIG. 2

RT-PCR products from mRNAs extracted from E. histolytica parasites cloned on soft agar with sense and antisense ariel primers (20). Lanes M, 100-bp ladders; lanes 1 to 5, different clones; lane 6, uncloned parent strain; lane 7, gDNA PCR product from the uncloned strain. Controls with a single sense or antisense ariel primer did not produce RT-PCR products (data not shown). The prominent 440-bp band corresponds to the ariel-1 gene, while lighter bands at lower molecular weights include those predicted by other ariel gene clones. Control RT-PCR with srehp, chit, and amebapore primers each produced a single product (data not shown) (6, 15, 25).

FIG. 3

Western blot of recombinant GST-Ariel with human antiamebic sera. Pooled human antiamebic sera reacted strongly with GST-Ariel repeats (Ar) and GST-E. histolytica ADH1 (Al), weakly with GST-E. histolytica chitinase repeats (Ch), and not at all with control GST (Co). Lane M, protein standards.