Characterization of the Noncovalent Interactions between Lysozyme and Panaxadiol Glycosides by Intensity-Fading – Matrix-Assisted Laser Desorption Ionization – Mass Spectrometry (IF-MALDI-MS)

Analyzing noncovalent interactions between notoginseng saponins and lysozyme by deposition scanning intensity fading MALDI-TOF mass spectrometry

Analysis of noncovalent interactions between natural products and proteins is important for rapid screening of active ingredients and understanding their pharmacological activities. In this work, the intensity fading MALDI-TOF mass spectrometry (IF-MALDI-MS) method with improved reproducibility was implemented to investigate the binding interactions between saponins from Panax notoginseng and lysozyme. The benchmark IF-MALDI-MS experiment was established using N,N',N″-triacetylchitotriose-lysozyme as a model system. The reproducibility of ion intensities in IF-MALDI-MS was improved by scanning the whole sample deposition with a focused laser beam. The relative standard deviation (RSD) of deposition scanning IF-MALDI-MS is 5.7%. Similar decay trends of the relative intensities of notoginseng saponins against increasing amounts of lysozyme were observed for all six notoginseng saponins. The half-maximal fading concentration (FC50) was calculated to quantitatively characterize the binding affinity of each ligand based on the decay curve. According to the FC50 values obtained, the binding affinities of the six notoginseng saponins were evaluated in the following order: notoginsenoside S > notoginsenoside Fc > ginsenoside Rb1 > ginsenoside Rd > notoginsenoside Ft1 > ginsenoside Rg1. The binding order was in accordance with molecular docking studies, which showed hydrogen bonding might play a key role in stabilizing the binding interaction. Our results demonstrated that deposition scanning IF-MALDI-MS can provide valuable information on the noncovalent interactions between ligands and proteins.

Imaging Method by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS) for Tissue or Tumor: A Mini Review

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an advanced technique that uses minimum fragmented ions from complex molecules for mass spectrometry (MS) analysis (tissue profiling by mass spectrometry). It is able to analyze spatially resolved tissue or tumor sections at the molecular level. It has become a valuable tool for tumor and tissue imaging, due to its ease of operation and high mass resolution, but it still has vast room for development in the instrumentation of larger proteins in some tissues. In this review, we focus on the main components of MALDI-MS instrumentation, sample handling and processing, the working principle of MALDI-MS, and its applications in diagnostic and prognostic assessments, tumor removal and drug development. Although it is less effective at detecting larger proteins in some tissues, it still shows huge potential because of its advancements in instrumentation and processing protocols. This article may benefit those who have interests in MALDI-MS for tissue or tumor imaging.

Lysozyme Improves the Inhibitory Effects of Panax notoginseng Saponins on Phenotype Transformation of Vascular Smooth Muscle Cells by Binding to Ginsenoside Re

Panax notoginseng saponins (PNS) have been used to treat cardiovascular diseases for hundreds of years in China. Lysozyme can bind to exogenous compounds and promote their activity. Nevertheless, knowledge of whether there is a synergistic role between lysozyme and PNS is far from sufficient. In this study, we show that the mixture of PNS and lysozyme synergistically inhibited platelet derived growth factor BB (PDGF-BB)-induced vascular smooth muscle cell (VSMC) viability, and in the five main components of PNS, GS-Re, but not GS-Rb1, NG-R1, GS-Rg1, or GS-Rd, reduced VSMC viability by combined application with lysozyme. Next, the supramolecular complexes formed by GS-Re and lysozyme were detected by mass spectrometry, and the binding ability increased with the concentration ratio of GS-Re to lysozyme from 4:1 to 12:1. In the supramolecular complexes, the relative contents of α-helix of lysozyme were increased, which was beneficial for stabilizing the structure of lysozyme. The 12:1 mixture of GS-Re and lysozyme (12.8 μmol/L GS-Re+1.067 μmol/L lysozyme) repressed PDGF-BB-induced VSMC viability, proliferation, and migration, which were associated with the upregulated differentiated markers and downregulated dedifferentiated markers. Finally, in CaCl₂-induced rodent abdominal aortic aneurysm (AAA) models, we found that the 12:1 mixture of GS-Re and lysozyme slowed down AAA progression and reversed phenotype transformation of VSMCs. Thus, Gs-Re combined with a small amount of lysozyme may provide a novel therapeutic strategy for vascular remodeling-associated cardiovascular diseases.