Insertion of L-Arginine in biomembranes of saturated and unsaturated lipids

HUGO A. PÉREZ; DISALVO, E.A.; FRÍAS, M.A.

Rosario

Congreso; L Reunión Anual de la Sociedad Argentina de Biofísica.; 2022

The interaction of proteins with cell membraneshas been explained in terms of the insertion of some amino acids at differentdepths of the bilayer. Some models postulate that such insertion is driven bythe partition of individual amino acids in the bilayer. In this sense,L-Arginine (Arg) is a positively charged amino acid constituent of peptides andproteins, participating in diverse mechanisms of protein–membrane interaction. Moleculardynamics studies have shown that Arg is solvated by water that penetrates theinner leaflet, leading to the so-called water pockets. The stability of thesewater defects seems to depend on membrane composition. Thus, the partition energetics assumesthat the interaction process of Arg with PCs implies the presence of water inthe membrane structure. Therefore, to understand the mechanism of peptideinsertion, it seems interesting to know the effect of isolated amino acids onthe lipid surface and the phase properties of membranes of lipid compositionwith different hydration profiles.In this work, the effect of Arg on thepolarity of lipid interphases of unilamellar vesicles (LUV) composed by1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-di-O- hexadecyl-sn-glycero-3-phosphocholine(DHPC) both in the gel and crystalline liquid (LC) phases and by1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (D9PC) was determined by measuring theGeneralized Polarization parameter (GP) using Laurdan as a probe. The results show that Arg increases themembrane polarization in saturated lipids in the LC state and decreases it inthe same state of unsaturated lipids (D9PC). In the absence of carbonyl groups(DHPC), GPex values decreased in both phase states indicating anincrease of polarity.These results would indicate that Arg can havedifferent effects on water properties at the interface of the membrane dependingit is formed by saturated lipids at high hydration, increasing thepolarizability of water molecules in that region. On the other hand, when thesystem is formed by D9PC that is in the LC phase, the insertion of Argincreases the GPex values, which suggests a decrease in free watermolecules. These results provide a new perspective on the interactions betweenamino acids and the composition of membranes.