The Study And Application On The Peptidoglycan Of Bifidobacteria To Bind Benzo (a) Pyrene

As a polycyclic aromatic hydrocarbon containing benzene rings,benzopyrene is widely distributed in the environment.It is a kind of highly active carcinogenic and mutagenic compound which has embryo toxicity.The presence of benzopyrene in food environment poses seriously harm to human health.The degradation of benzopyrene in human body is very slow,and the content of benzopyrene cannot be degraded to the safety level only by the metabolism of the body.To date,some studies showing that Lactobacillus and Bifidobacterium have a strong ability to bind many mutagenic compounds have been attracted attention.Their cell walls may play an important role in removing the mutagenic compounds.However,the study on the binding process of probiotic cell wall and benzopyrene was rather deficient.Therefore,the objects of this study were:(1)to construct the peptidoglycan structure model from Bifidobacterium by the Materials Studio;(2)to apply molecular docking and molecular dynamics methods to simulate the process of bifidobacterial benzopyrene-binding;and(3)to analyze the mechanism of the binding by HPLC and FTIR,and validate the adsorption model.The following are main results.1.The construction of peptidoglycan structure model which was constructed by Materials Studio visually showed that the composition of peptidoglycans depends on strains.The benzopyrene was all bound with bifidobacterial peptidoglycan via non-bonding forces,and the binding sites were related to the oxygen and nitrogen atoms.2.The adsorption rate of benzopyrene was tested by HPLC.Four bifidobacterial strains,i.e.,Bb-02,Bl-04,HN019 and Bi-26,showed high adsorption capacity to benzopyrene.The strains from the same species had a similar adsorption capacity to benzopyrene.As for the two strains of Bifidobacterium,the adsorption rate of strains HN019 and Bl-04 were higher than 70%.Their benzopyrene-binding rates were 74.37% and 76.02%,respectively.3.The structure of peptidoglycan before and after adsorption was analyzed by FTIR.FTIR analysis showed that the peptidoglycan extracted from the test strains had the similar structure to the standard peptidoglycan.It proved that the extracted peptidoglycan was identified as the bifidobacterial peptidoglycan.The adsorption site to benzopyrene was near the C-O bond of the alcohol and C-N bound of the amide in peptidoglycan.4.Peptidoglycan from strain Bl-04 was treated with HCl and then was bound with benzopyrene.The results showed that the percentage of peptidoglycan to bind benzopyrene increased from 75.96% to 92.80%.The simulation of peptidoglycan structure and adsorption showed that HCl treatment caused the structure and the steric stabilization of peptidoglycan to be changed,thus releasing more binding sites.The high consistency of the experimental results with those of computer dynamics proves that peptidoglycan from bifidobacteria is the key structure to affect the probiotics' ability to bind benzopyrene.The study was aimed to explain the binding of bifidobacterial and benzopyrene at a molecular level,and to provide a support for the removal of mutagenicity by bifidobacteria.At the present stage,the probiotics-related products are circulating in the market.