RESUMO
The 18. 5 kD myelin basic protein (MBP) isoform interacts with phospholipids and its role has been thought to maintain the stability and compactness of the myelin sheath structure. In this study, we describe the statistical thermodynamic theory of certain concentration effects on MBP in the majormyelin lipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethano-lamine (POPE), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine(POPS)) monolayers at the air/ subphase interface via the Langmuir-Blodgett (LB) technique. A simple statistical mechanical theory is established that predicts the interaction between proteins and phosphatehead groups at low surface pressures and the second virial coefficient dependences for the PC, PE, and PS head groups are illustrated. Two-dimensional virial equation of state (2D-VES) suggested that the interaction in the monolayer structure at the MBP-myelin interface is a repulsive force, and it induces a phase change in the monolayer. This is consistent with atomic force microscope (AFM) observations of domain and aggregate structures as well as with changes in the surface morphology induced by MBP. These analyses pertaining to membrane structures will provide a theoretical and experimental basis for the establishment of the myelin membrane modeling system.