Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Tuesday Speaker Abstracts

Interfacial Interactions with Cardiolipin-containing Membranes cause Cytochrome c's Peroxidase Activity Required for Mitochondrial Apoptosis without Unfolding the Protein. Patrick C. Van der Wel , Abhishek Mandal, Maria DeLucia, Jinwoo Ahn. University of Pittsburgh School of Medicine, Pittsburgh, USA. Background: Disease toxicity in Huntington’s Disease and many other neurodegenerative diseases is caused at least in part by mitochondrial dysfunction, increased reactive oxygen species, and increases in mitochondrial apoptosis. These lethal processes are connected by a proapoptotic gain-of-function in mitochondrial cytochrome c, which is induced by its binding to cardiolipin in the mitochondrial inner membrane. Formation of a cardiolipin-cytochrome-c complex turns the protein into a lipid peroxidase that generates cardiolipin-derived signaling molecules required for apoptosis to occur. Objective: Elucidate the structural changes that underlie the lethal peroxidase activity of cytochrome c induced by its binding to cardiolipin-containing membranes. Methods: We performed structural and functional studies of the peroxidase-active state of cytochrome c as it is bound to unilamellar cardiolipin-containing lipid vesicles. Fluorescence and other optical spectroscopies were combined with unprecedented 2D and 3D magic-angle- spinning solid-state NMR to probe the conformation and dynamics of the membrane-bound protein. Results: The vesicle-bound protein gains peroxidase activity in a cardiolipin-dependent fashion. Our structural measurements via magic-angle-spinning NMR and other techniques reveal that the membrane-bound protein retains the secondary structure and tertiary fold of its unbound native state. We also find that the protein interacts primarily with the surface of the lipid bilayers, without significantly disrupting the integrity of the lipid bilayer. Conclusions: Large-scale unfolding and penetration of the lipid bilayer are not required for cytochrome c’s membrane-induced peroxidase activity. Instead our data show that the protein gains peroxidase activity while bound to interface region of cardiolipin-containing vesicles as a peripherally bound protein that retain most of its native fold. Thus, the peroxidase activity appears to be more controlled and regulated than previously assumed, which may render it a viable and important target for disease modulation.

Liquid/Protein Interactions in Membrane Fusion and Fission Joshua Zimmerberg NIH, NICHD, USA No Abstract

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