Membrane orientation of the Na,K-ATPase regulatory membrane protein CHIF determined by solid-state NMR.

Corticosteroid hormone-induced factor (CHIF) is a major regulatory subunit of the Na,K-ATPase, and a member of an evolutionarily conserved family of membrane proteins that regulate the function of the enzyme complex in a tissue-specific and physiological-state-specific manner. Here we present the structure of CHIF oriented in the membrane, determined by solid-state NMR orientation-dependent restraints. Because CHIF adopts a similar structure in lipid micelles and bilayers, it is possible to assign the solid-state NMR spectrum measured for (15)N-labeled CHIF in oriented bilayers from the structure determined in micelles, to obtain the global orientation of the protein in the membrane.