Membrane Localization of a Myb3 Transcription Factor Regulated by a TvCyP1 Cyclophilin in the Parasitic Protozoan Trichomonas vaginalis.

In Trichomonas vaginalis, a TvCyP1 cyclophilin was previously demonstrated to regulate the nuclear translocation of Myb1 and Myb3, which respectively repress and activate transcription of an adhesion protein ap65-1 gene. In the present study, TvCyP1 was found to bind to Myb3 at sites spanning (54)Gly-Pro(55) and (72)Gly-Pro(73) with differential affinities. When Gly(54) and Gly(72) in Myb3 were both mutated, the mutant protein was restrained on outer membranes of hydrogenosomes and some cytoplasmic vesicles. In the purified Myb3 protein complex, a high molecular weight Myb3-interacting protein (Myb3IP(hmw)) and a 72-kDa heat shock protein (TvHSP72) were identified and characterized, with direct binding of Myb3 to Myb3IP(hmw) and TvHSP72 confirmed invitro. When cell lysates were fractionated by the differential and gradient centrifugations, TvCyP1 and Myb3 were always associated with membrane fractions enriched with Myb3IP(hmw) and Myb1, as well as hydrogenosomes and V-Myb organelle fractions. Mutations of Gly(54) and/or Gly(72) resulted in membrane redistribution of Myb3 and the aberrant assembly of the Myb3 protein complex. Consistent with these findings, the involvement of TvCyP1 in membrane distribution of Myb3, and dissociation of Myb3 from TvCyP1 protein complex were demonstrated, with direct interactions between TvCyP1 and Myb3IP(hmw) and that between TvCyP1 and TvHSP72, confirmed invitro. These observations suggest that TvCyP1 directly binds to Myb3 and some of its interacting proteins to mediate serial conformational switches of Myb3 for its transition from the membrane compartments toward the nucleus.