LOA LOA - STRUCTURAL DIVERSITY OF A 15-KDA REPETITIVE ANTIGEN

A ladder antigen of Loa loa was identified on Western blots of all lif e cycle stages probed with loaisis sera. The smallest subunit has a re lative M(r) of about 15 kDa and larger subunits represent size increme nts of 15.0 kDa. An 1800-bp genomic clone encoding this antigen was ch aracterized further by restriction mapping. Southern blot analysis, an d nucleotide sequencing. The antigen is encoded by multiple copies of a gene, linked in tandem repeats of 396 bp, each of which encodes 132 amino acids. These repeats have diverged sufficiently to produce disti nct restriction enzyme sites and Southern blot hybridization patterns. The 1764-bp insert contains no introns and encodes 588 amino acids, r epresenting one incomplete and four complete repeats. At the 3' end of three repeats, there are consensus proteolytic cleavage sites; one re peat has no cleavage site. Two perfect repeats show a 93.9% amino acid identity with one another; the rest of the repeats, despite being adj acent to one another, show only 31-42% identical amino acids. Putative asparagine N-linked glycosylation sites are expressed by only two of the repeats. Despite this structural diversity, each L. loa repeat sho wed homology to Ascaris suum allergen and the homologue protein descri bed in Dirofilaria immitis and Brugia pahangi. (C) 1995 Academic Press , Inc.