Prof. P. Nissen is an internationally recognized expert in protein biochemistry and serves as Vice-Dean for Research at the Faculty of Natural Sciences at Aarhus University. His research focuses on the structure of membrane proteins, and his achievements have been recognized with prestigious international awards.

 

Abstract: Na+,K+-ATPases establish and maintain the vital electrochemical gradients for Na+ and K+ across animal cell membranes. The protein is a ternary complex composed of α, β and FXYD subunits, of which isoforms that fine-tune transport properties are expressed in a tissue-specific fashion. We report cryo-EM structures under active ATPase turn-over conditions of the ubiquitously expressed human α1β1FXYD1 and neuron-specific α3β1FXYD1 isoform complexes reconstituted in lipid nanodiscs and probe their specific functional and biophysical properties [1]. The data provides an extensive insight into Na+-transport of ATP-activated enzyme through distinct conformational states, including a long-sought sodium-bound and ADP-released phosphoenzyme intermediate, denoted [Na3]E2P, which has so far been elusive to structural studies. It represents the critical transition from inward to outward oriented states ([Na3]E1P-ADP to ([Na3]E2P) and immediately precedes the voltage-sensitive step of Na+ release.

We discuss models for the formation and destabilization of co-operative Na+ binding at the ion-binding sites and how it affects cytoplasmic ion gating leading to Na+ dependent phosphorylation, and subsequently the onset of extracellular Na+ release from the [Na3]E2P state. 

The study also brings us to investigate and discuss the mechanism of differentiation in Na+ affinity of α3 compared to α1, which is physiologically important for how α3 becomes activated at elevated Na+ concentrations. Finally, we present the first structures of a disease-causing mutant form of α3, associated with Alternating Hemiplegia of Childhood (Q140L). The mutation compromises a specific phospholipid-binding pocket and impedes polyunsaturated phospholipid-mediated stimulation of Na+,K+-ATPase activity.