PENTAGONAL MODEL OF MEMBRANE CHANNEL OF NA,K-ATPASE - COMPUTER-SIMULATIONS OF STRUCTURE AND ELECTROSTATIC PROPERTIES

Computational modeling of the membrane channel of a sodium pump (Na,K- ATPase) is performed and the role of selected amino acids in binding o f sodium ions is discussed. The channel is build as a pentameric 10-he lix bundle. The transmembrane a-helices are determined from hydropathy calculations. The spatial arrangement of transmembrane a-helices is c hosen according to the size of a pore, intersegment loops geometry, an d orientation hydrophobicities of transmembrane segments. The latter p roperty provides the numerical estimate of the distribution of the hyd rophobic properties at the helical wheels. The model system involves t he peptide part and 150 water molecules that soak the pore. The channe l structure is submitted to geometry minimization and molecular dynami cs relaxation. The relative stability of the channel states with the n egatively charged acidic residues belonging to the pore interior decre ase in the order Glu-334 > Asp-810 > Glu-785 > Asp-814. The estimated binding energies of 1-3 Na+ ions with the channel with the ionized Glu -334 and Glu-785 amino acids are in the range allowing the exothermic complexation.