Physical interactions of fish protamine and antisepsis peptide drugs with bacterial membranes revealed by combination of specular x-ray reflectivity and grazing-incidence x-ray fluorescence

摘要

As a defined model of outer membranes of gram negative bacteria,we investigated the interaction of monolayersnof lipopolysacchrides from Salmonella enterica rough strains R90 (LPS Ra) with natural and synthetic peptides.nThe fine structures perpendicular to the membrane plane and the ion distribution near the interface were determinednby specular x-ray reflectivity (XRR) and grazing-incidence x-ray fluorescence (GIXF) in the presence andnabsence of divalent cations. The unique combination of XRR and GIXF allows for the quantitative identificationnof different modes of interactions in a high spatial resolution, which cannot be assessed by other experimentalnmethods. Natural fish protamine disrupts the stratified membrane structures in the absence of Ca2+ ions, whilenstaying away from the membrane surface in the presence of Ca2+ ions. In contrast, synthetic antisepsis peptidenPep 19-2.5 weakly adsorbs to the membrane and stays near the uncharged sugar units even in the absence ofnCa2+. In the presence of Ca2+, Pep 19-2.5 can reach the negatively charged inner core without destroying thenbarrier capability against ions.