The pi-Helix Formation between Asp(369) and Thr(375) as a Key Factor in E-1-E-2 Conformational Change of Na+/K+-ATPase
Abstract
Molecular modeling of the H-4-H-5-loop of the alpha(2) isoform of Na+/K+-ATPase in the E-1 and E-2 conformations revealed that twisting of the nucleotide (N) domain toward the phosphorylation (P) domain is connected with the formation of a short pi-helix between Asp(369) and Thr(375). This conformational change close to the hinge region between the N-domain and the P-domain could be an important event leading to a bending of the N-domain by 64.7 degrees and to a shortening of the distance between the ATP binding site and the phosphorylation site (Asp(369)) by 1.22 nm from 3.22 nm to 2.00 nm.
It is hypothesized that this shortening mechanism is involved in the Na+-dependent formation of the Asp(369) phospho-intermediate as part of the overall Na+/K+-ATPase activity.