S-layer proteins from lactobacilli increase rigidity of liposomes by counteracting the electrostatic repulsion

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

La Plata

Congreso; XXXVII Reuninón Anual de la Sociedad Argentina de Biofísica; 2008

Sociedad Argentina de Biofísica

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 to elucidate the mechanism by which S-layer proteins from lactobacilli are able to stabilize liposomes by hindering adhesion or fusion. Lateral pressure and z potential studies demosntrated that net positive charges are essential for S-layer recristalization process to occur on lipid membranes. In this condition, we studied the effects on liposomes rigidity and found that S-layer proteins from both lactobacilli increase the rigidity of liposomes by counteracting the electrostatic repulsion of the charges of stearyl amine molecules in the membrane surface plane. The diminution of the surface charge density of the SA positive charges by the S-layer proteins increases the packing of the acyl chains as observed with DPH anisotropy. This effect is similar to that observed in liposomes without positive charges (SL/cholesterol liposomes) or liposomes in which the positive charges of SA were neutralized at the membrane phase by equimolar negative charges of stearic acid. It is concluded that S-layer proteins by electrostatics forces induce a higher rigidity in the membrane phase that contributes to liposome stability. These results could be relevant for the use of these preparations as drug targeting and delivery systems for oral vaccines. It is concluded that S-layer attachment by electrostatics induces a higher rigidity in the membrane phase that contributes to liposome stability. These results could be relevant for the use of these preparations as drug targeting and delivery systems for oral vaccines