Can hopanoids modulate membrane properties like sterols do?

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

CABA

Simposio; Frontiers in bioscience 3; 2018

IBioBA-MPSP

In biological membranes, lipids play multiple roles andinfluence cell processes, either individually or collectively. Sterols arelipids that have the property of regulating dynamics and maintaining membranesin a microfluid state. Cholesterol is the major sterol in vertebrates,ergosterol plays a key role in fungi, and stigmasterol and sitosterol are themajor constituents of plants species.1 Hopanoids arepentacyclic compounds that are proposed to be sterol surrogates of primitivebacteria.2,3It has been suggested that the sterol modulationof the lipid order emerged as a critical evolutionary step ofbiological membranes allowing the cells to control their fluidity withoutcompromising their membrane integrity.4 Althoughprokaryotes lack sterols, it has been demonstrated that hopanoids can form liquid-ordered(Lo) phases in model membranes.3,5 In this manner, thecapacity of membranes to form Lo domains, and thus compartmentalize, may beoriginated before the earth oxygenation and the emergence of sterols and eukaryoteorganisms.3Despite having proved that Lo phase may be present in the membrane of organisms ofdifferent kingdoms, there still is a lack of systematic studies in which thedifferent sterols and hopanoids are compared together. In view of this, we haveparticular interest in developing a systematic platform to study how thepresence of sterols and hopanoids regulates the properties of model membranes. Thefirst step consists on evaluating the interfacial properties of films composedof pure sterols 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, inorder to evaluate if the different compounds promote the formation of a Lophase based on its distinctive characteristics: retaining of the fluidity whileincreasing the order of the hydrocarbon chains, and decreasing thepermeability. (1) Schaller, H. The Role of Sterols in PlantGrowth 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-Cyclopolyprenols on ?primitive? Membranes Made of PolyprenylPhosphates. Tetrahedron 2007, 63 (16), 3395?3407.(3) Saenz, J. P.;Sezgin, E.; Schwille, P.; Simons, K. Functional Convergence of Hopanoids andSterols in Membrane Ordering. 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 to Cholesterol: Structural Evolution andDifferential 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.