Only two of the Trichomonas vaginalis triplet AP51 adhesins are regulated by iron

Abstract

The sexually transmitted parasite Trichomonas vaginalis cytoadheres to the vaginal epithelium, and four candidate trichomonad adhesins have been identified. One such protein, termed AP51, was characterized further. To do this, we studied a 1 kb cDNA clone (AP51.2) isolated from a phagemid expression library, which encoded a fusion protein of approximately 38 kDa that was immuno-crossreactive with anti-AP51 serum and retained functional adhesive properties. We performed 5'-PCR amplification to recover the missing 5' end in order to provide the complete cDNA sequence for the gene encoded by AP51.2 (ap51-2). Other PCR products revealed almost complete sequences for two additional ap51 genes, making AP51 a member of a multigene family of at least three distinct proteins and genes. The ap51-1 and ap51-3 genes each encoded for 407 amino acids while ap51-2 encoded 408 amino acids, and not unexpectedly, these genes had a high percent identity at the DNA and amino acid levels. Mapping confirmed the sequence distinctions and uniqueness of the three ap51 genes. Southern analysis using gene-specific probes revealed the single copy nature of each of the ap51 genes, all of which were present among the numerous agar clones of single trichomonads of the isolates tested. Importantly, Northern analysis showed transcriptional regulation by iron of only the ap51-1 and ap51-3 genes but not ap51-2, perhaps indicating the presence of two bona fide isoforms of the ap51 genes. The 3'-untranslated region of ap51-3 had a short poly (A) tail as well as the sequence motif AUUUA, which may relate to differential degradation of ap51-3 transcripts, in comparison to ap51-1 and ap51-2. Finally, the ap51 genes had partial homology to the beta-subunit of succinyl-CoA synthetase, reinforcing the idea that molecular mimicry may play a role in host parasitism by T. vaginalis.