Biophysical exploration of protein–flavonol recognition: effects of molecular properties and conformational flexibility

Abstract

The current work explores the biomolecular recognition of a series of flavonols by a protein and then uncovers the influences of the structural features of flavonols and the protein's own characteristics, e.g. the dynamics and flexibility, on the bioavailability of flavonols by using the pivotal biomacromolecule hemoglobin as a model. The experimental results revealed that flavonol may lead to a notable decrease in the steady-state fluorescence intensity of the β-37 Trp residue, and in the meantime the R-T transition of the protein transpired. Such noncovalent recognition forms the ground-state adduct, with an association intensity of 3.991 × 10(4) M(-1) in the reaction process, which has already been authenticated by the detailed analysis of time-resolved fluorescence and UV/vis absorption spectra. Furthermore, flavonol can form hydrogen bonds and π-conjugation effects with several amino acid residues on the polypeptide chain, for example, Trp-37, Arg-40, Asp-99 and Asn-102, and this event would induce self-regulation of the compact, regular conformation of the protein to a certain extent, which explicitly corroborates the results of circular dichroism. According to the study of molecular docking and structure-activity relationships, we could see that the recognition capacities of the protein-flavonols are inversely interrelated with the C log P values of the flavonol molecules. Moreover, the properties of the substituents in the structural B-ring unit of flavonols, i.e. polarity, position and number, will also prominently affect the degree of affinity and bioavailability of the protein-flavonol complexes. The analytical results of molecular dynamics (MD) simulation testified that the discussions of the structure-activity relationships are entirely logical, and the conformations of the amino acid residues forming noncovalent interactions tend to be stable in the MD simulation, as further elucidated from the dynamics data. Plainly, molecular recognition of the protein-flavonols might noticeably cause relatively large changes in protein flexibility, and then manifest different recognition strengths and corresponding biological activities. This issue will be carefully validated by the interpretation of root-mean-square fluctuation.

Deciphering the Interaction of 5,7‐Dihydroxyflavone with Hen‐Egg‐White Lysozyme through Multispectroscopic and Molecular Dynamics Simulation Approaches

“…The notable reduction in the Trp emission intensity of HEWL upon addition of chrysin could be attributed to the occurrence of specific biochemical interaction between HEWL and chrysin which indicates that chrysin resides within the substrate binding site where Trp 62, 63 and 108 are located or it forms direct non‐covalent interactions with the aromatic Trp residues . Further, the emission profile of chrysin in the absence and presence of HEWL is also illustrated in the inset of Figure .…”

In vitro interactions of esculin and esculetin with bovine hemoglobin alter its structure and inhibit aggregation: insights from spectroscopic and computational studies

“…Similar findings have been reported for rutin, quercetin, and morin with BHb. 18,54 Another observation made was a slight blue shift of the emission maxima was seen as the concentration of the coumarins increased. This suggested the environment near the dominant fluorophore was exposed to a more hydrophobic environment in the presence of the coumarin derivatives.…”

Inhibition of amyloid formation of bovine hemoglobin by bioactive phenolic acids: an elaborate investigation into their binding properties with the protein using multi-spectroscopic and computational techniques

“…2), providing evidence of a successful biomolecular association taking place between FA/CA/CGA and β 2- Trp37 through the formation of non-covalent bonds or the phenolic acids residing within the vicinity of β 2- Trp37. 70 Well-established literature studies reiterate that the emission intensity of a protein can be reduced due to numerous molecular interactions arising from energy transfer, molecular rearrangement, excited-state reactions, and quenching mechanisms. 71 As the ligands possess a considerable amount of absorbance at λ ex = 295 nm and λ em = 337 nm of BHb, inner filter effect (IFE) correction of the emission profiles was carried out using the following equation (eqn (1)).…”