The interaction mechanism of papain and bromelain with apigenin and luteolin in binary and ternary systems

In this study, the interaction mechanism of papain and bromelain with apigenin and luteolin in binary and ternary systems was compared and analyzed by spectroscopic methods, molecular docking, and molecular dynamics simulation. Additionally, the effects of apigenin and/or luteolin on the conformational changes and enzymatic activity of papain and bromelain were investigated. The results show that apigenin and/or luteolin exhibit a moderate binding affinity with papain/bromelain, with the binding constants Ka in the range of 104-105 L mol-1. The order of addition of apigenin and luteolin significantly influenced their binding affinities to the enzymes. The main non-covalent forces of the papain-luteolin (first)-apigenin ternary system are hydrogen bonds and Van der Waals forces. Hydrophobic interactions, electrostatic forces and hydrogen bonds are the main non-covalent forces of other binary and ternary systems. These systems differentially alter the microenvironment of Trp and Tyr residues, secondary and tertiary structures, and enzymatic activity. Molecular docking and dynamics simulations identified specific binding sites of apigenin and/or luteolin on papain/bromelain, corroborating experimental findings. Notably, the ternary system exhibits a stronger inhibitory effect on papain activity compared to binary systems.

Study on the interaction between active components from traditional Chinese medicine and plasma proteins

Traditional Chinese medicine (TCM), as a unique form of natural medicine, has been used in Chinese traditional therapeutic systems over two thousand years. Active components in Chinese herbal medicine are the material basis for the prevention and treatment of diseases. Research on drug-protein binding is one of the important contents in the study of early stage clinical pharmacokinetics of drugs. Plasma protein binding study has far-reaching influence on the pharmacokinetics and pharmacodynamics of drugs and helps to understand the basic rule of drug effects. It is important to study the binding characteristics of the active components in Chinese herbal medicine with plasma proteins for the medical science and modernization of TCM. This review summarizes the common analytical methods which are used to study the active herbal components-protein binding and gives the examples to illustrate their application. Rules and influence factors of the binding between different types of active herbal components and plasma proteins are summarized in the end. Finally, a suggestion on choosing the suitable technique for different types of active herbal components is provided, and the prospect of the drug-protein binding used in the area of TCM research is also discussed.

In vitro evaluation of the cytotoxic and bactericidal mechanism of the commonly used pesticide triphenyltin hydroxide

Triphenyltin hydroxide (TPTH) is a widely used pesticide that is highly toxic to a variety of organisms including humans and a potential contender for the environmental pollutant. In the present study, the cytotoxic mechanism of TPTH on mammalian cells was analyzed using HeLa cells and the antibacterial activity was analyzed using B. subtilis and E. coli cells. TPTH inhibited the growth of HeLa cells with a half-maximal inhibitory concentration of 0.25 μM and induced mitotic arrest. Immunofluorescence microscopy analysis showed that TPTH caused strong depolymerization of interphase microtubules and spindle abnormality with the appearance of colchicine type mitosis and condensed chromosome. TPTH exhibited high affinity for tubulin with a dissociation constant of 2.3 μM and inhibited the in vitro microtubule assembly in the presence of glutamate as well as microtubule-associated proteins. Results from the molecular docking and in vitro experiments implied that TPTH may have an overlapping binding site with colchicine on tubulin with a distance of about 11 Å between them. TPTH also binds to DNA at the A-T rich region of the minor groove. The data presented in the study revealed that the toxicity of TPTH in mammalian cells is mediated through its interactions with DNA and its strong depolymerizing activity on tubulin. However, its antibacterial activity was not through FtsZ, the prokaryotic homolog of tubulin but perhaps through its interactions with DNA.