Self-homodimerization of an actinoporin by disulfide bridging reveals implications for their structure and pore formation

PAZOS, ISABEL FABIOLA; DE FREITAS, SONIA MARIA; BARBOSA, JOÃO ALEXANDRE RIBEIRO GONÇALVES; SOUZA, ADOLFO CARLOS BARROS; LIMA, JÔNATAS CUNHA BARBOSA; MARTINS-DE-SA, DIOGO; DE ARMAS-GUITART, GERMAN; HERVIS, YADIRA DE LA PATRIA; CANET, LIEM; PÉREZ-SOCAS, LUIS BENITO; VALLE, AISEL

Scientific Reports

Nature Publishing Group

Año: 2018 vol. 8

The Trp111 to Cys mutant of sticholysin I, an actinoporin from Stichodactyla helianthus sea anemone, forms a homodimer via a disulfide bridge. The purified dimer is 193 times less hemolytic than the monomer. Ultracentrifugation, dynamic light scattering and size-exclusion chromatography demonstrate that monomers and dimers are the only independent oligomeric states encountered. Indeed, circular dichroism and fluorescence spectroscopies showed that Trp/Tyr residues participate in homodimerization and that the dimer is less thermostable than the monomer. A homodimer three-dimensional model was constructed and indicates that Trp147/Tyr137 are at the homodimer interface. Spectroscopy results validated the 3D-model and assigned 85° to the disulfide bridge dihedral angle responsible for dimerization. The homodimer model suggests that alterations in the membrane/carbohydrate-binding sites in one of the monomers, as result of dimerization, could explain the decrease in the homodimer ability to form pores.