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

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.

Deciphering anti-biofilm property of Arthrospira platensis-origin peptides against Staphylococcusaureus

Arthrospira platensis is a valuable natural health supplement consisting of various types of vitamins, dietary minerals, and antioxidants. Although different studies have been conducted to explore the hidden benefits of this bacterium, its antimicrobial property has been poorly understood. To decipher this important feature, here, we extended our recently introduced optimization algorithm (Trader) for aligning amino acid sequences associated with the antimicrobial peptides (AMPs) of Staphylococcus aureus and A.platensis. As a result, similar amino acid sequences were identified, and several candidate peptides were generated accordingly. The obtained peptides were then filtered based on their potential biochemical and biophysical properties, and their 3D structures were simulated based on homology modeling techniques. Next, to investigate how the generated peptides can interact with S. aureus proteins (i.e., heptameric state of the hly and homodimeric form of the arsB), molecular docking approaches were used. The results indicated that four peptides included better molecular interactions relative to the other generated ones in terms of the number/average length of hydrogen bonds and hydrophobic interactions. Based on the outcomes, it can be concluded that the antimicrobial property of A.platensis might be associated with its capability in disturbing the membrane of pathogens and their functions.

Evolutionary Analysis of the Lysine-Rich N-terminal Cytoplasmic Domains of the Gastric H+,K+-ATPase and the Na+,K+-ATPase

The catalytic α-subunits of both the Na⁺,K⁺-ATPase and the gastric H⁺,K⁺-ATPase possess lysine-rich N-termini which project into the cytoplasm. Due to conflicting experimental results, it is currently unclear whether the N-termini play a role in ion pump function or regulation, and, if they do, by what mechanism. Comparison of the lysine frequencies of the N-termini of both proteins with those of all of their extramembrane domains showed that the N-terminal lysine frequencies are far higher than one would expect simply from exposure to the aqueous solvent. The lysine frequency was found to vary significantly between different vertebrate classes, but this is due predominantly to a change in N-terminal length. As evidenced by a comparison between fish and mammals, an evolutionary trend towards an increase of the length of the N-terminus of the H⁺,K⁺-ATPase on going from an ancestral fish to mammals could be identified. This evolutionary trend supports the hypothesis that the N-terminus is important in ion pump function or regulation. In placental mammals, one of the lysines is replaced by serine (Ser-27), which is a target for protein kinase C. In most other animal species, a lysine occupies this position and hence no protein kinase C target is present. Interaction with protein kinase C is thus not the primary role of the lysine-rich N-terminus. The disordered structure of the N-terminus may, via increased flexibility, facilitate interaction with another binding partner, e.g. the surrounding membrane, or help to stabilise particular enzyme conformations via the increased entropy it produces.