A study of the antibacterial mechanism of catechins: Isolation and identification of Escherichia coli cell surface proteins that interact with epigallocatechin gallate

Catechins have high anti-bacterial activity against various microorganisms. In this study, the mechanism of anti-bacterial activity of catechins was investigated using Escherichia coli. Transmission electron microscope analysis revealed that deposits containing EGCg were found only on the outer membrane, which is the outermost layer of the cell surface, in E. coli cells treated with EGCg. Based on this observation, we focused on outer membrane proteins as targets of EGCg in E. coli. Two-dimensional electrophoresis identified 16 spots that had disappeared or showed markedly reduced intensity after treatment with EGCg compared to the control. Of these, an outer membrane porin protein, OmpG, acids suggested that the basic amino acids Lys, Arg, and His strongly interacted with EGCg. The docking simulation with EGCg and OmpG revealed that EGCg enters into the porin pore and binds to Arg residues present on the inner surface of the pore channel through hydrogen bonding, resulting in inhibition of the porin function. Furthermore, glucose uptake by E. coli was inhibited in cells treated with EGCg. Taken together, these results suggest that EGCg inhibits the major function of porin proteins, namely the passive transport of small hydrophilic molecules such as glucose, leading to growth inhibition of E. coli.