The oxidized phospholipid PazePC promotes permeabilization of mitochondrial membranes by Bax
2016 (English)In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1858, no 6, 1288-1297 p.Article in journal (Refereed) Published
Mitochondria play a crucial role in programmed cell death via the intrinsic apoptotic pathway, which is tightly regulated by the B-cell CLL/lymphoma-2 (Bcl-2) protein family. Intracellular oxidative stress causes the translocation of Bax, a pro-apoptotic family member, to the mitochondrial outer membrane (MOM) where it induces membrane permeabilization. Oxidized phospholipids (OxPls) generated in the MOM during oxidative stress directly affect the onset and progression of mitochondria-mediated apoptosis. Here we use MOM-mimicking lipid vesicles doped with varying concentrations of 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC), an OxPl species known to significantly enhance Bax-membrane association, to investigate three key aspects of Bax's action at the MOM: 1) induction of Bax pores in membranes without additional mediator proteins, 2) existence of a threshold OxPl concentration required for Bax-membrane action and 3) mechanism by which PazePC disturbs membrane organization to facilitate Bax penetration. Fluorescence leakage studies revealed that Bax-induced leakage, especially its rate, increased with the vesicles' PazePC content without any detectable threshold neither for OxPl nor Bax. Moreover, the leakage rate correlated with the Bax to lipid ratio and the PazePC content. Solid state NMR studies and calorimetric experiments on the lipid vesicles confirmed that OxPl incorporation disrupted the membrane's organization, enabling Bax to penetrate into the membrane. In addition, 15N cross polarization (CP) and insensitive nuclei enhanced by polarization transfer (INEPT) MAS NMR experiments using uniformly 15N-labeled Bax revealed dynamically restricted helical segments of Bax embedded in the membrane, while highly flexible protein segments were located outside or at the membrane surface.
Place, publisher, year, edition, pages
2016. Vol. 1858, no 6, 1288-1297 p.
Apoptosis, Bax-protein, Calorimetry, Membranes, NMR, Oxidized phospholipids, Leakage
Research subject Biochemistry; Physical Chemistry
IdentifiersURN: urn:nbn:se:umu:diva-110699DOI: 10.1016/j.bbamem.2016.03.003ISI: 000375356900023OAI: oai:DiVA.org:umu-110699DiVA: diva2:864257
Originally published in manuscript form with the title The oxidized phospholipid PazePC promotes the formation of Bax pores in mitochondrial membranes2015-10-262015-10-262016-07-01Bibliographically approved