Structural insights into the pore forming mechanism by actinoporins

BELLOMIO A; MECHALY AE; GIL-CARTÓN D; MORANTE K; VALLE M; GUÉRIN DM; GONZALEZ-MAÑAS JM

Los Cocos, Córdoba

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Biofísica; 2009

Sociedad Argentina de Biofísica

Actinoporins belong to the á-helical barrel family of pore forming toxins (PFTs). These toxins are secreted by sea anemones as weapons to permeabilize cell membranes for both,defense and attack purposes. Fragaceatoxin C (FraC) is a new actinoporin, as other members of the PFTs family, it is proposed that the mechanism by which permeabilize target membranes is a multi-step process. Initially, the toxin is secreted as soluble monomers that binds preferently sphingomyelin containing membranes. At the membrane surface oligomerizes forming a non-lytic crown-like structure composed of 8/9 subunits. Finally, toxin inserts an amphiphatic helix located at its N-terminus leading to the final pore conformation in a process that depends on the coexistence of lipidic phases to form the transmembrane á-helical barrel pore. Based on the nonameric crystal structure of FraC in complex with a non-ionic detergent (LDAO) and cryo-EM 3D reconstructions of toxin at model membranes, here we show that FraC pore formation process could involve at least 3 membrane bound states. 1- A non-lytic oligomer with its N-ter still attach to the toxin core. 2- A non-lytic conformation in which the N-terminal amphipatic helix dettachs from the toxin core and transiently resides at membrane-water interface. 3- A fully assembly pore with its N-terminus inserted into the bilayer.