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Pore Formation by a Bax-Derived Peptide: Effect on the Line Tension of the Membrane Probed by AFM

Ana J. García-Sáez ^*, Salvatore Chiantia ^*, Jesús Salgado  and Petra Schwille ^*

^* Biotechnologisches Zentrum der TU Dresden, Dresden, Germany; and Instituto de Ciencia Molecular, Universitat de València, Burjassot, Spain

Correspondence: Address reprint requests to Petra Schwille, Tatzberg 47-51, 1307 Dresden, Germany. Tel.: 49-351-4634-0328; E-mail: petra.schwille{at}biotec.tu-dresden.de.

Bax is a critical regulator of physiological cell death that increases the permeability of the outer mitochondrial membrane and facilitates the release of the so-called apoptotic factors during apoptosis. The molecular mechanism of action is unknown, but it probably involves the formation of partially lipidic pores induced by Bax. To investigate the interaction of Bax with lipid membranes and the physical changes underlying the formation of Bax pores, we used an active peptide derived from helix 5 of this protein (Bax-5) that is able to induce Bax-like pores in lipid bilayers. We report the decrease of line tension due to peptide binding both at the domain interface in phase-separated lipid bilayers and at the pore edge in atomic force microscopy film-rupture experiments. Such a decrease in line tension may be a general strategy of pore-forming peptides and proteins, as it affects the energetics of the pore and stabilizes the open state.

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