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BH3 interacting domain death agonist (Bid), a pro-apoptotic member of the Bcl-2 family of proteins, is activated through cleavage by caspase-8. The active C-terminal fragment of Bid (tBid) translocates to the mitochon-dria where it interacts with cardiolipins at contact sites and induces the release of cytochromecby a mechanism that is not yet fully understood. | ễFEBS Journal Interaction of the alpha-helical H6 peptide from the pro-apoptotic protein tBid with cardiolipin Patrice X. Petit1 Pauline Dupaigne2 Fabrizio Pariselli1 Francois Gonzalvez1 Francois Etienne2 Carole Rameau2 and Sophie Bernard2 1 Institut Cochin INSERM U567 CNRS UMR8104 Université Paris Descartes France 2 UPR 2228 CNRS Universite Paris Descartes France Keywords apoptosis Bid cardiolipin membrane mitochondria Correspondence S. Bernard UPR 2228 CNRS Universite Paris Descartes IFR 95 45 rue des Saints-Peres 75006 Paris France Fax 33 1 4286 2042 Tel 33 1 4286 2046 E-mail sophie.bernard@parisdescartes.fr Received 25 June 2009 revised 28 August 2009 accepted 2 September 2009 doi 10.1111 j.1742-4658.2009.07345.x BH3 interacting domain death agonist Bid a pro-apoptotic member of the Bcl-2 family of proteins is activated through cleavage by caspase-8. The active C-terminal fragment of Bid tBid translocates to the mitochondria where it interacts with cardiolipins at contact sites and induces the release of cytochrome c by a mechanism that is not yet fully understood. It has been shown that the alpha-helices aH6 and aH7 which create the hairpin-forming domain of tBid mediate the insertion of Bid into mitochondrial membranes and are essential for the cytochrome c-releasing activity. In the present study we focused on the interaction between the aH6 and the mitochondrial membrane. By the use of single-cell electropermeabiliza-tion associated with flow cytometric analysis of intact cells we demonstrated that H6 is able to induce cell death when used in the micromolar range. We also studied the interactions of the aH6 with artificial monolayers. We showed that the presence of negatively charged cardiolipins greatly enhances the insertion of aH6 into the phospholipid monolayer. The modification of two charged amino acid residues in aH6 abolished its insertion and also its in vivo effects. Furthermore the negative values of the excess areas of mixing indicate that .
