Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Thursday Speaker Abstracts

Dynamic Interactions of Protein Elements of the Bacterial Division Machinery Evidenced in Phospholid Bilayer Nanodiscs Victor Hernandez-Rocamora 1,3 , Silvia Zorrilla 1 , Carlos Alfonso 1 , Allen Minton 2 , Miguel Vicente 1 , German Rivas 1 . 1 CSIC, Madrid, Spain, 2 NIH, Bethesda, MD, USA, 3 Newscastle University, Newscastle, United Kingdom. The first molecular assembly of the bacterial division machinery is the proto-ring, which in E. coli is formed as a result of the anchoring of FtsZ (a self-assembling GTPase ancestor of cytoskeletal tubulin) to the cytoplasmic membrane by the action of FtsA (an amphitropic protein) and ZipA (a bitopic membrane protein) [1]. We have studied the activities, interactions and assembly properties of FtsZ in ZipA-containing nanodiscs by means of analytical ultracentrifugation and fluorescence-based techniques, combined with electron microscopy and biochemical assays [2]. Nanodiscs are structures formed by a membrane scaffold protein encirciling a phospholipid bilayer, which can incorporate membrane proteins preserving their natural properties while behaving as soluble entities [3]. These results have been exploited to optimize the reconstitution of proto-ring elements in giant vesicles [4,5] to gain new insights into the precise functions of protoring elements in cell division events. [1] Rico et al. 2013. J Biol Chem 288:20830-20836 [2] Hernández-Rocamora et al. 2012. J Biol Chem 287:30097-30104 [3] Hernández-Rocamora et al. 2014. Curr Opin Med Chem

[4] Cabré et al. 2013. J Biol Chem 288:26625-26634 [5] Rivas et al. 2014. Curr Opin Chem Biol 22:18-26

What Cholesterol is Doing in the Plasma Membrane Philip L. Yeagle . University of Connecticut, Storrs/Mansfield, USA.

The molecular basis for the essential role of specific sterols in supporting particular cell growth (for example, cholesterol in mammalian cells and ergosterol in yeast cells) has long been the object of intense interest. Cholesterol modulates the function of particular mammalian membrane proteins critical to cellular function. Ergosterol modulates the activity of particular yeast membrane proteins. Experimental data support primarily two mechanisms for this modulation by sterols. In one mechanism, the requirement of "free volume' by integral membrane proteins for conformational changes as part of their functional cycle is antagonized by the presence of high levels of cholesterol in the membrane. This results from the membrane ordering promoted by cholesterol. In the other mechanism, the sterol modulates membrane protein function through direct sterol-protein interactions. Sterols bind to the membrane protein and act as effectors modulating protein activity. Biochemical experiments show binding of cholesterol to some membrane proteins. Recent X-ray crystal structures of some of these same proteins reveal the details of the cholesterol binding site. This mechanism provides an explanation for the modulation of the activity of important membrane proteins and for the essential requirement of a structurally-specific sterol for cell viability.

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