Use of small angle neutron scattering to study the interaction of angiotensin II with model membranes

Understanding biological processes assumes a detailed understanding of the interaction of all involved molecules. Here the effect of the peptide hormone angiotensin II (Ang II), an agonist of the angiotensin receptors, on the structure of unilamellar and multilamellar dimyristoyl phosphatidylcholine vesicles was studied by small angle neutron scattering, dynamic light scattering and differential scanning calorimetry. The calorimetry data indicate a weak interaction of Ang II with the surface of the membrane bilayer, as the pretransition persists during all experiments, and the main transition is only slightly shifted towards higher temperatures. From the SANS data we were able to confirm the calorimetric data and verify the interaction of the hormone with the membrane surface. At low temperatures, when the lipid molecules are in the gel phase, more precisely in the ripple phase, the peptide penetrates in the head group core, but due to the close packing of the acyl chains, the hydrophobic region is not affected. In a temperature region below but close to the region of the phase transition, the hydrophibic core starts to be affected by the peptide, and the same is true for the fluid phase. Upon binding of the peptide, the thickness of the head group increases, and the scattering length density of the head group starts to rise with increasing peptide concentrations. This interaction and binding to the membrane surface may be relevant for the relocation, binding and reconstitution of the angiotensin receptors into the membrane. Second, the peptide adsorption to the membrane surface may contribute to the binding of Ang II in the active site of the receptor.