Synthesis of Tailed Metalloporphyrins Modified with 2-Chloronicotinic Acid and Interactions with Human Serum Albumin

Differences between the binding modes of enantiomers S/R-nicotine to acetylcholinesterase

Nicotine causes neurotoxic effects because it quickly penetrates the blood–brain barrier after entering the human body. Acetylcholinesterase (AChE) is a key enzyme in the central and peripheral nervous system associated with neurotoxicity. In this study, a spectroscopic method and computer simulation were applied to explore the mode of interaction between AChE and enantiomers of nicotine (S/R-nicotine). Fluorescence spectroscopy showed that the quenching mechanism of endogenous fluorescence of AChE by S/R-nicotine was static, as confirmed by the time-resolved steady-state fluorescence. The binding strength of both nicotine to AChE was weak (S-AChE: K_a = 80.06 L mol⁻¹, R-AChE: K_a = 173.75 L mol⁻¹). The main driving forces of S-AChE system interaction process were van der Waals force and hydrogen bonding, whereas that of R-AChE system was electrostatic force. Computer simulations showed that there were other important forces involved. S/R-Nicotine had a major binding site on AChE, and molecular docking showed that they bound mainly to the cavities enclosed by the active sites (ES, PAS, OH, AACS, and AP) in the protein. UV-vis spectroscopy and 3D spectroscopy indicated that nicotine significantly affected the microenvironment of Trp amino acids in AChE. The CD spectra indicated that S-nicotine increased the α-helical structure of AChE, but the overall conformation did not change significantly. By contrast, R-nicotine significantly changed the secondary structure of AChE. 5,5′-Dithiobis-2-nitrobenzoic acid (DTNB) method indicated that S and R nicotine produced different degrees of inhibition on the catalytic activity of AChE. Both experimental methods and computer simulations showed that R-nicotine had a significantly higher effect on AChE than S-nicotine. This research comprehensively and systematically analyzed the mode of interaction between nicotine and AChE for neurotoxicity assessment.

Study on the binding modes of AChE to S/R-nicotine.

Metalloporphyrin-based porous polymers prepared via click chemistry for size-selective adsorption of protein

Zinc porphyrin-based porous polymers (PPs-Zn) with different pore sizes were prepared by controlling the reaction condition of click chemistry, and the protein adsorption in PPs-Zn and the catalytic activity of immobilized enzyme were investigated. PPs-Zn-1 with 18 nm and PPS-Zn-2 with 90 nm of pore size were characterized by FTIR, NMR and nitrogen absorption experiments. The amount of adsorbed protein in PPs-Zn-1 was more than that in PPs-Zn-2 for small size proteins, such as lysozyme, lipase and bovine serum albumin (BSA). And for large size proteins including myosin and human fibrinogen (HFg), the amount of adsorbed protein in PPs-Zn-1 was less than that in PPs-Zn-2. The result indicates that the protein adsorption is size-selective in PPs-Zn. Both the protein size and the pore size have a significant effect on the amount of adsorbed protein in the PPs-Zn. Lipase and lysozyme immobilized in PPs-Zn exhibited excellent reuse stability.

Exploring the binding pattern between pepsin and deferasirox using detailed experimental and computer simulation methods

Steady-state fluorescence spectroscopy indicated that a ground state complex was formed between deferasirox (DFX) and pepsin. The binding parameters and thermodynamic parameters of pepsin–DFX complex formation suggested the presence of only one high affinity binding site in the binding process of DFX and pepsin and that the binding process was hydrogen bond dominated. According to the MD simulation optimal pepsin–DFX binding model analysis, the binding force between DFX and pepsin was mainly hydrogen bonding, and the hydrophobic interaction was supplemented. Synchronous fluorescence spectroscopy and 3D fluorescence spectroscopy indicated that the binding of DFX to pepsin had minor effect on the protein structure and function. Circular dichroism spectra showed that DFX had no significant effect on the main secondary structure of pepsin. MD analysis also showed that DFX did not affect the looseness of pepsin and the overall secondary structure, but it affected the amino acid residue sequence Leu48-Ala49-Cys50-Ser51-Asp52. Pepsin enzyme activity test showed that the addition of DFX had a slight enhancement effect on the activity of pepsin. Combined with the MD results, DFX bound to pepsin and was closer to the pepsin active site Asp-215, which may affect the electrical environment of Asp-215 residues and enhance the activity of pepsin.

Investigation on the binding properties of deferasirox to pepsin.