Influence of the electric charge of the mitochondrial outer membrane on the orientation and binding of the pro-apoptotic protein Bax during the activation and oligomerization processes.

OMAR JAURE; DIEGO OBIOL; FERNANDO ZAMARREÑO; MARCELO D. COSTABEL

San Luis

Congreso; XLVIII Reunión anual de la Sociedad Argentina de Biofísica; 2019

Sociedad Argentina de Biofísica

The crucial event that triggers apoptosis is the activation and translocation to themitochondrial outer membrane of the pro-apoptotic Bax protein. In healthy cells Bax isfound as an inactive monomer in the cytosol or weakly bound to membranes. A transientinteraction between Bax and the Bid protein or its truncated version tBid would cause itsactivation. Once activated, Bax functional regulation includes: conformational change,translocation to the mitochondrial outer membrane and changes in the state ofaggregation (formation of dimers and multimers). The oligomerization of Bax leads topermeabilization of the mitochondrial outer membrane, pore formation and the releasefrom the intermembrane space of apoptogenic factors, thus triggering a series of eventsthat culminates in cell death.In order to deepen our knowledge in the regulation of the mitochondrial pathway ofapoptosis, we carried out an analysis of the electrostatic component and the trajectoriesof molecular dynamics of the system formed by Bax (monomeric and oligomeric states),Bid, tBid and the mitochondrial membrane. The results obtained demonstrate theinfluence of electrostatic interactions between membrane and the monomeric andoligomeric Bax pro-apoptotic protein; and between Bax and the activator protein Bid/tBid. In addition we determined optimal interaction distances, influence of the ionicstrength of the medium, analyzed the distribution of charges in the macromolecules andorientation of the macrodipoles.The information obtained allowed us to establish an activation model that shows theinfluence of charged phospholipids on the interaction of Bax with membrane before andafter its activation by the Bid/tBid protein. This information, together with theidentification of the amino acids involved in the first contact of Bax with the membraneand with its protein counterpart, by means of analysis of specific mutations, made itpossible to detect potential modes of interaction that must be further analyzed todetermine their importance in the activation of the mitochondrial pathway of apoptosis.