APPLICATION OF 3-DIMENSIONAL MOLECULAR HYDROPHOBICITY POTENTIAL TO THE ANALYSIS OF SPATIAL-ORGANIZATION OF MEMBRANE DOMAINS IN PROTEINS .3. MODELING OF INTRAMEMBRANE MOIETY OF NA+, K+-ATPASE

The most probable interlocation of transmembrane alpha-helices of Na+, K+-ATPase has been calculated by a computer-aided molecular simulation approach in the framework of models with eight and 10 helical peptides for the alpha-subunit. The method is based on the concept or three-dimensional molecular hydrophobicity potential (MHP) and provides valuable description of spatial hydrophobic properties of membrane-spanning segments as well as helix - helix packing interactions inside the membrane. Resulting model of the arrangement of intramembrane domain agrees with recent results on hydrophobic photolabeling of an intramembrane part of the beta-subunit and the sixth transmembrane segment of the alpha-subunit. It is also consistent with current ideas on hydrophobic organization of integral membrane proteins. Possible topology of a cation-binding site is discussed.