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BspA and Pmp proteins of Trichomonas vaginalis mediate adherence to host cells

Trichomonas vaginalis is one of the most widespread, sexually transmitted pathogens. The infection involves a morphological switch from a free-swimming pyriform trophozoite to an amoeboid cell upon adhesion to host epithelial cells. While details on how the switch is induced and to what proteins of the host surface the parasite adheres remain poorly characterized, several surface proteins of the parasite itself have been identified as potential candidates. Among those are two expanded protein families that harbor domains that share similarity to functionally investigated surface proteins of prokaryotic oral pathogens; these are the BspA proteins of Bacteroidales and Spirochaetales, and the Pmp proteins of Chlamydiales. We sequenced the transcriptomes of five Trichomonads and screened for the presence of BspA and Pmp domain-containing proteins and tested the ability of individual T. vaginalis candidates to mediate adhesion. Here we demonstrate that (i) BspA and Pmp domain-containing proteins are specifically expanded in T. vaginalis in comparison to other Trichomonads, and that (ii) individual proteins of both families have the ability to increase adhesion performance in a non-virulent T. vaginalis strain and Tetratrichomonas gallinarum, a parasite usually known to infect birds but not humans. Our results initiate the functional characterization of these two broadly distributed protein families, whose origin we trace back to the origin of Trichomonads themselves.