Trypsin inhibition by Ligupurpuroside B as studied using spectroscopic, CD, and molecular docking techniques

Abstract

It is well known that Ligupurpuroside B is a water-soluble polyphenolic compound and used to brew bitter tea with antioxidant activities. It acted as a stimulant to the central nervous system and a diuretic (increase the excretion of urine), was used to treat painful throat and high blood pressure, and also exerted weight-loss function. In this regard, a detailed investigation on the mechanism of interaction between Ligupurpuroside B and trypsin could be of great interest to know the pharmacokinetic behavior of Ligupurpuroside B and for the design of new analogues with effective pharmacological properties. Ligupurpuroside B successfully quenched the intrinsic fluorescence of trypsin via static quenching mechanism. The binding constants (K_a) at three temperatures (288, 298, and 308 K) were 1.7841 × 10⁴, 1.6251 × 10⁴ and 1.5483 × 10⁴ L mol⁻¹, respectively. Binding constants revealed the stronger binding interaction between Ligupurpuroside B and trypsin. The number of binding sites approximated to one, indicating a single class of binding for Ligupurpuroside B in trypsin. The enzyme activity result suggested that Ligupurpuroside B can inhibit trypsin activity. Thermodynamic results revealed that both hydrogen bonds and hydrophobic interactions play main roles in stabilization of Ligupurpuroside B-trypsin complex. Circular dichroism (CD) results showed that the conformation of trypsin changed after bound to ligupurpuroside B. Molecular docking indicated that Ligupurpuroside B can enter the hydrophobic cavity of trypsin and was located near Trp215 and Tyr228 of trypsin.

Communicated by Ramaswamy H. Sarma

Keywords:

• Fluorescence
• trypsin
• Ligupurpuroside B
• circular dichroism
• molecular docking

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (Grant 31540012, 31470431, 30570421, 81501213), Guangdong Natural Science Foundation for Major cultivation project (2014A030308017), Guangdong Natural Science Foundation (2016A030313051), Shenzhen Science and Technology Innovation Committee Grants (JSGG20160229120821300, JCYJ20150625103526744, JCYJ20170302144535707, JCYJ20120613112512654, JCYJ20140414090541801, JSGG20130411160539208, KQCX20140522111508785, CXZZ20150601110000604, ZDSYS201506031617582), Shenzhen special funds for Bio-industry development (NYSW20140327010012), and Shenzhen Medical Scientific Research Project (201401077).