Cell Physiology and Molecular Biophysics
Assistant Professor of Cell Physiology
Texas Tech University Health Sciences Center
3601 4th Street, STOP 6551
Lubbock, Texas 79430
Phone: (806) 743-3170
FAX: (806) 743-1512
Our research focuses on understanding the function, mechanisms and pharmacology of the proteins that transport ions across the membrane. They are essential for the electrical signaling in the cardiovascular and nervous systems, and as such, they represent the target of several pharmacological agents used for the treatment of a number of cardiovascular and neural diseases.
We have two main projects to address two specific goals: first, elucidating the relationship between the structure, the function, and the mechanism of the Na/K pump; second, elucidating how the physical properties of the lipid bilayer influence the function and pharmacology of cardiac ion transporting proteins embedded in this lipidic matrix.
Survival of most animal cells requires maintenance of the electrochemical gradients of Na+ and K+ ions across the plasma membrane by the Na/K pump. Through a series of conformational changes, this heterodimeric (α + β) membrane protein catalyzes the extrusion of 3 Na+, in exchange for 2 K+, using the energy released by hydrolysis of one ATP molecule. The Na/K pump is the target of digitalis, a group of drugs widely used for more than 200 years for the treatment of congestive heart failure.
To elucidate the structural basis of the function and pharmacology of the Na/K pump, we use a combination of molecular biological (site-directed mutagenesis and heterologous expression), electrophysiological (standard and giant patch-clamp, two-electrode and cut-open oocyte voltage clamp) and biochemical (chemical modification, measurements of ATPase activity, etc.) methods.
Membrane-protein interaction and mechanisms of drug action
Many amphipathic compounds affect the function of many different membrane proteins, such as Ca, Na, K and Cl channels, Na/Ca exchanger, and Na/K pump, with similar concentration dependence. Some of these "unspecific" drugs are ingested by humans, either as medicines or with food.
Membrane proteins are embedded in a lipid bilayer matrix. To avoid exposure of hydrophobic groups to the polar environment, the span of the hydrophobic tails of both leaflets must match the length of the hydrophobic residues of the protein in contact with the bilayer. Thus, when a protein conformation requires those two lengths to differ, the hydrophobic mismatch forces the bilayer to deform, with an energetic cost determined by the bilayer's material properties (elasticity, curvature, etc.). Drugs that interact with the bilayer may affect protein function by changing this energetic cost. We use gramicidin channels (pore forming antibiotic peptides) incorporated in biological membranes, as reporters of these bilayer physical properties. We expect to gain insight on the mechanism of drug action by comparing the effect of these unspecific drugs on gramicidin channel activity with the effects on "typical" ion transporting proteins.
Yu H, Ratheal IM, Artigas P, Roux B (2011) Protonation of key acidic residues is critical for the K(+)-selectivity of the Na/K pump. Nat Struct Mol Biol. [Epub ahead of print]
Ratheal I, Virgin G, Yu H, Roux B, Gatto C, Artigas P (2010). Selectivity of externally facing ion binding sites in the Na/K pump to alkali metals and organic cations. Proc Natl Acad Sci U S A. 107:18718-23
Yaragatupalli S, Olivera JF, Gatto C, and Artigas P (2009) Altered Na+ transport after an intracellular alpha-subunit deletion reveals strict external sequential release of Na+ from the Na/K pump. Proc Natl Acad Sci U S A. 106:15501-15512.
Gadsby DC, Takeuchi A, Artigas P, Reyes N. (2009). Review. Peering into an ATPase ion pump with single-channel recordings. Philos Trans R Soc Lond B Biol Sci. 364:229-38
Takeuchi A, Reyes N, Artigas P, Gadsby DC. (2008). The ion pathway through the opened Na(+),K(+)-ATPase pump. Nature 456:413-6
Rakowski RF, Artigas P, Palma F, Holmgren M, De Weer P, and Gadsby DC. (2007). Sodium flux ratio in Na/K pump-channels opened by palytoxin. J. Gen. Physiol. 130:41-54
Artigas P, Hobart EA, Díaz L, Al’Aref SJ, Straw S, Sakaguchi M, and Andersen OS. (2006). 2,3 butanedione monoxime affects CFTR channel function through phosphorylation-dependent and phosphorylation-independent Mechanisms. The role of bilayer material properties. Mol. Pharmacol. 70:2015-2026.
Artigas P and Gadsby DC. (2006). Ouabain affinity determining residues lie close to the Na/K pump ion pathway. Proc. Natl. Acad. Sci. 103:12613-12618.