Elsevier

Food Chemistry

Volume 243, 15 March 2018, Pages 118-124
Food Chemistry

Characterization of binding interactions between selected phenylpropanoid glycosides and trypsin

https://doi.org/10.1016/j.foodchem.2017.09.118Get rights and content

Highlights

  • The inhibitory effects of four selected PPGs against trypsin were investigated.

  • The number/position of the phenolic OH groups affect the interaction and inhibition.

  • The structure of trypsin was altered due to its interaction with the PPGs.

Abstract

Phenylpropanoid glycosides (PPGs) are important bioactive polyphenolic compounds that are widely distributed in plants. In this paper, the inhibitory effects of four selected PPGs against trypsin were investigated. The interactions between these PPGs and trypsin were further investigated by multiple spectroscopic methods and molecular docking studies. The results showed that the binding of each of these PPGs to trypsin induced changes in the natural conformation of trypsin, which inhibited the enzyme in the following order: acteoside > syringalide A 3′-α-l-rhamnopyranoside > lipedoside A-I > osmanthuside B. The binding constant (Ka) values followed the same trend. The hydrogen bond force played an important role in the interaction between each PPG and trypsin. Interestingly, the binding affinity and inhibitory effect increased as the number of phenolic hydroxyl groups increased. In addition, the effect of the phenolic hydroxyl group on the A ring had a greater effect than one on the B ring.

Introduction

Trypsin, a type of serine protease, plays an important role in digestion. The inhibition of this digestive enzyme may reduce the absorption of nutrients. On the other hand, reducing the activity of this type of enzyme may be considered for the treatment of diseases such as pancreatitis, rheumatoid arthritis, cystic fibrosis, asthma, platelet aggregation disorders, and pulmonary emphysema (Brandl et al., 2016, Leung et al., 2000).

Polyphenols are secondary metabolites in seeds, fruits, and vegetables and are the most abundant antioxidants in the human diet (Cohen & Kennedy, 2010). Polyphenols have been investigated intensively due to their potential health-beneficial effects on humans (Mushtaq & Wanim, 2013). However, polyphenols can also exhibit a negative role by blocking nutrient absorption, which is caused by their interactions with digestive enzymes (Ozdal, Capanoglu, & Altay, 2013). To optimize the biological utilization of polyphenols for human nutrition, knowledge of the interaction between polyphenols and trypsin is desirable.

Phenylpropanoid glycosides (PPGs) are important bioactive polyphenolic compounds that are distributed in a variety of plants as well as foods of plant origin (Pan, Yuan, Lin, Jia, & Zheng, 2004) and are associated with a wide range of biological activities (Chen et al., 2002; Díaz et al., 2004; Wang, Li, Ma, Zhang, & Jia, 2013; Zhang et al., 2008). A previous investigation has shown that PPGs from Ligustrum robustum inhibit trypsin activity due to their binding to this enzyme (Wu, Wang, et al., 2013). However, the detailed binding interactions and structure–activity relationships between PPGs and trypsin are not clear.

The different structures of polyphenols significantly affect their binding process with digestive enzymes (Ozdal et al., 2013). In this study, we selected four PPGs (acteoside, syringalide A 3′-α-l-rhamnopyranoside, lipedoside A-I, and osmanthuside B) with the same carbon skeleton and different numbers and positions of the phenolic hydroxyl groups to evaluate their inhibitory activity against trypsin. We used CD, FTIR, and fluorescence spectroscopy as well as molecular docking studies to help characterize the nature of binding between the PPGs and trypsin. Furthermore, structure–activity relationship analyses were conducted to elucidate the binding interactions between these four different PPGs and trypsin. This study may provide useful information for further revealing the mechanisms behind the interactions between PPGs and trypsin.

Section snippets

Materials

Bovine trypsin (2500 U/mg), casein, and N-α-benzoyl-l-arginine 4-nitroanilide hydrochloride (BAPNA) were from Sigma-Aldrich Co. (St. Louis, MO, USA). Trypsin solution (1.0 × 10−4 M) was prepared in 0.05 M phosphate-buffered saline (PBS, pH 7.5). All other chemicals were of analytical grade.

Extraction and determination of PPGs

The PPGs were extracted as described (He et al., 2003). In brief, dry leaves (1.2 kg) of L. purpurascens were extracted with 10 L hot EtOH 2 times under reflux; the extract was concentrated in a rotary evaporator

Trypsin inhibitory activity

The PPGs were evaluated as trypsin inhibitors according to their IC50 values. The PPGs inhibited trypsin in the following order: acteoside (91 ± 4.32 μg/mL) > syringalide A 3′-α-l-rhamnopyranoside (167 ± 6.38 μg/mL) > lipedoside A-I (200 ± 7.56 μg/mL) > osmanthuside B (481 ± 5.45 μg/mL). Acteoside has four phenolic hydroxyl groups, syringalide A 3′-α-l-rhamnopyranoside and lipedoside A-I have three phenolic hydroxyl groups, and osmanthuside B has two phenolic hydroxyl groups. The results suggested that the

Conclusion

In this study, four selected PPGs with the same carbon skeleton and different numbers of phenolic hydroxyl groups were evaluated for their inhibitory activity against trypsin. The spectroscopic results and docking studies determined that these four different PPGs, through binding to trypsin, changed the conformation of trypsin, thus resulting in inhibition of trypsin activity. The hydrogen bond force played an important role in the interaction between each PPG and trypsin. The order of binding

Acknowledgments

This study was supported in part by research funding from the Natural Science Funding of China (no 31670360), the Natural Science Funding of Guangdong Province (no. 2015A030313558), the Technological Research Funding of Guangdong Province (no. 2015A010107017), and the Research Funding of Shenzhen (nos. JCYJ20140418091413497, CXZZ20150529165110750, CXZZ20150601110000604, ZDSYS201506031617582 and KQCX20140522111508785).

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