The Trichomonas vaginalis phenotypically varying P270 immunogen is highly conserved except for numbers of repeated elements

Abstract

The prominent and phenotypically variable immunogenic protein of Trichomonas vaginalis, termed P270, is present in all isolates. Most, if not all, patients make antibody to the DREGRD epitope contained in the 333 bp tandemly repeating element (TRE). The complete sequence of p270 of a fresh clinical isolate was recently derived (Musatovova and Alderete, Microb Pathogen 1998; 24: 223-39). We hypothesized that the size polymorphisms of P270 were due to the varied number of TREs that comprise a large, central portion of the gene. In this study, we analysed the p270 coding regions of ten representative isolates. It was determined also that the sequence of the TRE of different p270 genes shared > or =99% identity, and individual TREs of the same p270 gene showed them to have identical nucleotide sequences, affirming the highly-conserved nature of this element within each gene. The coding regions upstream and downstream of the central TREs were then generated by PCR amplification using specific primers. The PCR products corresponding to the 5' and 3'-end coding, non-repeat sequences were then subjected to restriction analyses, and the regions were highly conserved for all p270 genes. The complete sequence of two p270 genes showed > or = 99% identity of amino acids at the N- and C-terminal regions of p270, further reinforcing that the reported polymorphisms in Mr of P270 is due to the varying number of TREs and, therefore, the size of the TRE domain. In support of this hypothesis and during these analyses, one isolate, T. vaginalis T016, was discovered which possessed a p270 gene with only one partial repeat unit. Importantly, and as with all other p270 genes, transcription of this single-repeat p270 gene in isolate T016 was confirmed. The start codon for the p270 T016 gene was preceded by the 12 nucleotide consensus Inr promoter-like sequence (TCATTTTTAATA) and possessed a putative transmembrane domain at the carboxy terminus.