Self-Association of Enolase from Trichomonas vaginalis. Monomers, Dimers, and Octamers Coexist in Solution

We used small-angle X-ray scattering to study the self-association of enolase from Trichomonas vaginalis as a function of the protein concentration and cosolute type. We observed coexisting monomers, dimers, and octamers in variable relative populations, depending on whether Tris-acetate, Tris-HCl, or potassium phosphate buffers were used. Phosphate ions hindered the formation of dimers and octamers. In contrast, the populations of dimers and octamers increased in Tris-acetate or Tris-HCl buffers and additionally increased by augmenting protein concentration or adding magnesium. Single oligomeric species could not be isolated in any of the experimental conditions tested. Furthermore, the secondary and tertiary structures, as well as the temperature-induced denaturation of the mixtures of species, were investigated. The acquired species lost enzymatic activity, but they were prone to interact with plasminogen, as judged from changes in the secondary and tertiary structures upon complex formation.