Structural and conformational changes concomitant with the E1–E2 transition in H<SUP>+</SUP>K<SUP>+</SUP>-ATPase: a comparative protein modeling study

Comparative modeling studies on conserved regions of the gastric H+K+-ATPase reveal that the E1–E2 conformational transition induces significant tertiary structural changes while conserving the secondary structure. The residues 516–530 of the cytoplasmic domain and TM10 within the transmembrane (TM) regions undergo maximum tertiary structural changes. The luminal regions exhibit comparatively lesser tertiary structural deviations. Residues 249–304 show maximum secondary structural deviation in the conformational transition. The Cys-815 and Cys-323 residues involved in inhibitor binding are found to have smaller buried side chain areas in the E1 conformation compared to E2. Retention of activity correlates well with the buried side chain area when selected amino acid residues in TM6 are mutated using modeling techniques with bulkier amino acid residues. Conformational specificity for ion binding is corroborated with the fraction of side chains exposed to polar atoms of the residues E345, D826, V340, A341, V343, and E822