LOCALIZATION OF LIGAND INTERACTIONS WITH THE SODIUM PUMP

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DESCRIPTION (Applicant's abstract): The objective of this work is to obtain a more complete understanding of how the sodium pump protein or Na,K-ATPase carries out its essential physiological role, the active transport of Na and K ions across the cellular plasma membrane. Experimental studies over the past several decades have established relationships between the transport reactions which this intrinsic membrane protein mediates and the biochemical reactions associated with the transport. The protein couples the transport of Na and K to the hydrolysis of ATP and how this coupling is achieved is a central issue in transport physiology. It has been established that there are separate regions of the protein responsible for cation transport and ATP binding and hydrolysis. We have proposed that a conformational coupling occurs between these two domains and experiments to be carried out will test this proposal. Specific postulates have been made about movements in the various parts of the protein and the present program of work will test these proposals The methods used will combine heterologous expression of the sheep renal Na,K-ATPase in insect cells, which do not usually possess this protein, together with protein chemistry and fluorescent labelling. The studies will also seek to explain the precise role of the beta-subunit in the active transport process. The sodium pump is vital in a variety of organs for fluid and electrolyte balance and excitability, and is the specific target of digitalis, the most widely used therapy in cardiac insufficiency. Before an adequate description of the pathological states involving fluid and electrolyte imbalance or an understanding of how digitalis works can be achieved we need to have an adequate description of the functioning sodium pump. The studies to be carried out are aimed at providing such a description. An understanding of the mechanism of the Na,K-ATpase will also be invaluable in accounting for the mechanism of the other members of the P-type ATPase superfamily.