The castling between hopanoids and sterols in membranes

AGUSTÍN MANGIAROTTI; CHRISTOPH A. NAUMANN; ELIDA NAHIR PUENTES; DARÍO MARTÍN GENOVESE; NATALIA WILKE

La Plata

Jornada; III Encuentro de Jóvenes Biofísicos Latinoamericanos: Biophysics for the Young and the restless; 2018

Young Initiative on Biophysics

            In biologicalmembranes, lipids play multiple roles and thereby influence cell processes,either individually or collectively. The sterols are lipids that have theproperty of regulating dynamics and maintaining membranes in a microfluidstate. While cholesterol is the major sterol in vertebrates, ergosterol plays akey role in fungi, and stigmasterol and sitosterol are the major constituentsof sterol profiles of plants species.1 Hopanoids are pentacycliccompounds that are proposed to be sterol surrogates of primitive bacteria.2,3            It has been proposed that the sterolmodulation of the lipid order emerged as a critical evolutionary step ofbiological membranes allowing the cells to control their fluidity withoutcompromising their membrane integrity.4 Although prokaryotes lacksterols, it has been demonstrated that hopanoids can form liquid-ordered (lo)phases in model membranes.3,5 In this manner, the capacity ofmembranes to form Lo domains, and thus compartmentalize, may be originatedbefore the earth oxygenation and the emergence of sterols and eukaryoteorganisms.3            Despite having proved that lo phasemay be present in the membrane of organisms of different kingdoms, there stillis a lack of systematic studies in which the differences and similitudes betweenthe different sterols and hopanoids are evaluated together. In view of this, wehave particular interest in developing a systematic platform to study thepresence of sterols and hopanoids that regulate the properties of modelmembranes with liquid-liquid phase coexistence. The first step consists onevaluating the interfacial and diffusional properties of films composed of puresterols and the hopanoid diplopterol. The aim of this study lies in thecomparison of the molecular behavior at the air-water interface. The secondstep describes binary and ternary lipid mixtures in monolayers and bilayers.This evaluates if the different compounds promote the formation of aliquid-ordered phase based on its distinctive characteristics: retaining of thefluidity while increasing the order of the hydrocarbon chains and decreasingthe permeability. (1)      Schaller, H. The Role of Sterols inPlant Growth and Development. Prog. Lipid Res. 2003, 42 (3), 163?175.(2)      Ribeiro, N.; Streiff, S.; Heissler,D.; Elhabiri, M.; Albrecht-Gary, A. M.; Atsumi, M.; Gotoh, M.; Désaubry, L.;Nakatani, Y.; Ourisson, G. Reinforcing Effect of Bi- and Tri-Cyclopolyprenolson ?primitive? Membranes Made of Polyprenyl Phosphates. Tetrahedron 2007, 63(16), 3395?3407.(3)      Saenz, J. P.; Sezgin, E.; Schwille,P.; Simons, K. Functional Convergence of Hopanoids and Sterols in MembraneOrdering. Proc. Natl. Acad. Sci. 2012, 109 (35), 14236?14240.(4)      Miao, L.; Nielsen, M.; Thewalt, J.;Ipsen, J. H.; Bloom, M.; Zuckermann, M. J.; Mouritsen, O. G. From Lanosterol toCholesterol: Structural Evolution and Differential Effects on Lipid Bilayers.Biophys. J. 2002, 82 (3), 1429?1444.(5)      Sáenz, J. P.; Grosser, D.; Bradley,A. S.; Lagny, T. J.; Lavrynenko, O.; Broda, M.; Simons, K. Hopanoids asFunctional Analogues of Cholesterol in Bacterial Membranes. Proc. Natl.Acad. Sci. U. S. A. 2015, 112 (38), 11971?11976.