A study on the protease activity and structure of pepsin in the presence of atenolol and diltiazem

Pepsin, as the main protease of the stomach, plays an important role in the digestion of food proteins into smaller peptides and performs about 20% of the digestive function. The role of pepsin in the development of gastrointestinal ulcers has also been studied for many years. Edible drugs that enter the body through the gastrointestinal tract will interact with this enzyme as one of the first targets. Continuous and long-term usage of some drugs will cause chronic contact of the drug with this protein, and as a result, the structure and function of pepsin may be affected. Therefore, the possible effect of atenolol and diltiazem on the structure and activity of pepsin was studied. The interaction of drugs with pepsin was evaluated using various experimental methods including UV-Visible spectroscopy, fluorescence spectroscopy, FTIR and enzymatic activity along with computational approaches. It was showed that after binding of atenolol and diltiazem to pepsin, the inherent fluorescence of the protein is quenched. Determination of the thermodynamic parameters of interactions between atenolol and diltiazem with pepsin indicates that the major forces in the formation of the protein-drug complexes are hydrophobic forces and also atenolol has a stronger protein bonding than diltiazem. Additional tests also show that the protease activity of pepsin, decreases and increases in the presence of atenolol and diltiazem, respectively. Investigation of the FTIR spectrum of the protein in the presence and absence of atenolol and diltiazem show that in the presence of atenolol the structure of protein has slightly changed. Molecular modeling studies, in agreement with the experimental results, confirm the binding of atenolol and diltiazem to the enzyme pepsin and show that the drugs are bind close to the active site of the enzyme. Finally, from experimental and computational results, it can be concluded that atenolol and diltiazem interact with the pepsin and change its structure and protease activity.