Effects of surface charges and cholesterol on the interactions between S-layer proteins and lipid monolayers

HOLLMANN, AXEL; DELFEDERICO, LUCRECIA; DE ANTONI, GRACIELA; SEMORILE, LILIANA; DISALVO, ANIBAL

Buzios, Brasi

Congreso; VII Iberoamerican Congress of Biophysics; 2009

One of the commonly observed outer surface components of cell envelops of prokaryotic organisms, archaea and bacteria are crystalline arrays of proteinaceous subunits, known as surface layers. In previous work, we showed that S-layer proteins from Lactobacillus kefir and Lactobacillus brevis are able to stabilize liposomes prepared with lecithin-cholesterol and stearylamine. The adsorption of S-layer proteins to positively charged liposomes was evidenced by the shift of the z potential towards negative values and electron microscopy. The aim of the present work was evaluate the interactions between S-layer proteins with lipids monolayer composed of different ratio of soy-been lecithin, cholesterol and stearylamine. Surface pressure studies demonstrated that both proteins from L. brevis and L. kefir are able to increase the surface pressure after be injected in the subphase of lipid monolayer. The interactions by addition of aqueous soluble S-layer protein are P0 dependent an increase were surface pressure are lower indicating that interaction became more stringer when the lipid monolayer are less structure as expected for soluble proteins. When the ratio of cholesterol was change we observed that the surface pressure was higher when the amount of cholesterol decrees, indicating that S-layer proteins interact more strongly with monolayer became more fluidity, beside that the cut off was the same in all curves.  Finally to establish the relation between charges of head polar lipids and protein recristalización we change the ratio of stearylamine on the lipid monolayer. The surface pressure variations obtained were significantly lower and the cut off obtained was lower too. Previously report for another soluble protein (Martini, Biochim Biophys Acta, 2007) showed the cut off of the curves appears related to the head group of the lipid specie and the slope are related with the depends on the nature of the acyl chain in a good agreement with our results.