Bioinformatic Study of Possible Acute Regulation of Acid Secretion in the Stomach

Abstract

The gastric H⁺,K⁺-ATPase is an integral membrane protein which derives energy from the hydrolysis of ATP to transport H⁺ ions from the parietal cells of the gastric mucosa into the stomach in exchange for K⁺ ions. It is responsible for the acidic environment of the stomach, which is essential for digestion. Acid secretion is regulated by the recruitment of the H⁺,K⁺-ATPase from intracellular stores into the plasma membrane on the ingestion of food. The similar amino acid sequences of the lysine-rich N-termini α-subunits of the H⁺,K⁺- and Na⁺,K⁺-ATPases, suggests similar acute regulation mechanisms, specifically, an electrostatic switch mechanism involving an interaction of the N-terminal tail with the surface of the surrounding membrane and a modulation of the interaction via regulatory phosphorylation by protein kinases. From a consideration of sequence alignment of the H⁺,K⁺-ATPase and an analysis of its coevolution with protein kinase C and kinases of the Src family, the evidence points towards a phosphorylation of tyrosine-7 of the N-terminus by either Lck or Yes in all vertebrates except cartilaginous fish. The results obtained will guide and focus future experimental research.

Keywords: Amino acid sequence analysis; Electrostatic switch mechanism; Gastric proton pump; Mirror tree analysis; Protein kinase C; Src kinase.

Fig. 1

Sequence alignment of the N-terminus of the α₁ isoform of the catalytic α-subunit of the gastric H⁺,K⁺-ATPase from vertebrates. Residues which are conserved across all species are highlighted in yellow. Tyrosine 7 (Y), which is conserved in all vertebrates except cartilaginous fish, is highlighted in light blue.The numbering of the residues is based on the H. sapiens sequence. The species have been grouped according to classes. i.e., placental mammals (orange, top), marsupial mammals (blue), reptiles (green), amphibians (pink), bony fish (grey) and cartilaginous fish (pale yellow, bottom)

Fig. 2

Correlations of evolutionary distances between common organisms expressing various isoforms of PKC and the H⁺,K⁺-ATPase α₁-subunit. Each data point represents a combination of a pair of common organisms for each protein, as explained in the Materials and Methods section. Hence, there are many more data points than common organisms. For comparison, the top row of the figure shows correlations of a positive control, the α₁-subunit of the H⁺,K⁺-ATPase with the β₁-subunit of the H⁺,K⁺-ATPase followed by two negative controls, i.e., PKCα with EGFR followed by hexokinase with the H⁺,K⁺-ATPase α₁ subunit

Fig. 3

Correlations of evolutionary distances between common organisms that express different members of the Src kinase family of enzymes and the H⁺,K⁺-ATPase α₁-subunit. Each data point represents a combination of a pair of common organisms for each protein, as explained in the Materials and Methods section