Interaction betweenPlectranthus barbatusherbal tea components and human serum albumin and lysozyme: Binding and activity studies

Anti-cholinesterase and antioxidant active constituents ofPlectranthus barbatusaqueous extract were found in plasma of rats after its administration – rosmarinic acid, luteolin and apigenin. The aim of the present work is to determine if the extract components can interact with human plasma proteins, namely albumin and lysozyme. Protein intrinsic fluorescence analysis showed that the plant phenolic compounds may bind to albumin, the main transport protein in plasma, and to lysozyme. The estimated thermodynamic parameters suggest that the main intermolecular interaction is hydrophobic association. FTIR analysis of the protein amide bands showed that the plant extract components do not alter the secondary structure of either albumin or lysozyme, however the rate of hydrogen–deuterium exchange suggests that tertiary structure changes might have occurred. An increase of hydrogen deuterium exchange suggests that rosmarinic acid may bind to the fatty acid binding sites in albumin, while luteolin and apigenin may bind to the drug binding sites. The plant extract components also inhibit lysozyme activity with IC50values around 100 μM. ThereforeP. barbatusherbal tea, rosmarinic acid, luteolin and apigenin interact and may be transported by albumin and lysozyme. The inhibition of lysozyme activity may be an additional mechanism for its anti-inflammatory activity.

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Conformational changes in gastric H+/K+-ATPase monitored by difference Fourier-transform infrared spectroscopy and hydrogen/deuterium exchange

Biochemical Journal ◽

10.1042/bj20040277 ◽

2004 ◽

Vol 382 (1) ◽

pp. 121-129 ◽

Cited By ~ 20

Author(s):

Frantz SCHEIRLINCKX ◽

Vincent RAUSSENS ◽

Jean-Marie RUYSSCHAERT ◽

Erik GOORMAGHTIGH

Keyword(s):

Fourier Transform ◽

Secondary Structure ◽

Conformational Changes ◽

Tertiary Structure ◽

Structural Information ◽

Deuterium Exchange ◽

Attenuated Total Reflection ◽

Hydrogen Deuterium Exchange ◽

Hydrogen Deuterium ◽

Difference Fourier

Gastric H+/K+-ATPase is a P-type ATPase responsible for acid secretion in the stomach. This protein adopts mainly two conformations called E1 and E2. Even though two high-resolution structures for a P-ATPase in these conformations are available, little structural information is available about the transition between these two conformations. In the present study, we used two experimental approaches to investigate the structural differences that occur when gastric ATPase is placed in the presence of various ligands and ligand combinations. We used attenuated total reflection–Fourier-transform IR experiments under a flowing buffer to modify the environment of the protein inside the measurement cell. The high accuracy of the results allowed us to demonstrate that the E1–E2 transition induces a net change in the secondary structure that concerns 10–15 amino acid residues of a total of 1324 in the proteins. The E2.K+ structure is characterized by a decreased β-sheet content and an increase in the disordered structure content with respect to the E1 form of the enzyme. Modifications in the absorption of the side chain of amino acids are also suggested. By using hydrogen/deuterium-exchange kinetics, we show that tertiary-structure modifications occurred in the presence of the same ligands, but these changes involved several hundreds of residues. The present study suggests that conformational changes in the catalytic cycle imply secondary-structure rearrangements of small hinge regions that have an impact on large domain re-organizations.

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