Phe475 and Glu446 but not Ser445 participate in ATP-binding to the alfa-subunit of NA/K-ATPase

Abstract

The ATP-binding site of Na+/K+-ATPase is localized on the large cytoplasmic loop of the small alpha, Greek-subunit between transmembrane helices H4 and H5. Site-directed mutagenesis was performed to identify residues involved in ATP binding.

On the basis of our recently developed model of this loop, Ser445, Glu446, and Phe475 were proposed to be close to the binding pocket. Replacement of Phe475 with Trp and Glu446 with Gln profoundly reduced the binding of ATP, whereas the substitution of Ser445 with Ala did not affect ATP binding.

Fluorescence measurements of the fluorescent analog TNP-ATP, however, indicated that Ser445 is close to the binding site, although it does not participate in binding

Keywords

• NA/K-ATPase
• Fluorescence spectroskopy
• ATP-binding site
• TNP-ATP