Spectroscopic and Molecular Docking Investigation on the Interaction of Cumin Components with Plasma Protein: Assessment of the Comparative Interactions of Aldehyde and Alcohol with Human Serum Albumin

Abstract

The interaction of the important plasma protein, human serum albumin (HSA), with two monoterpenes found in cumin oil, i.e., cuminaldehyde (4-isopropylbenzaldehyde) and cuminol (4-isopropylbenzyl alcohol), was studied in this paper. Both experimental and computational methods were utilized to understand the mechanism of binding. The UV absorption profile of HSA changes in the presence of both cuminaldehyde and cuminol, due to the interaction between HSA with both monoterpenes. The intrinsic fluorescence intensity of HSA was also quenched on the sequential addition of both ligands, due to change in the microenvironment of the fluorophore present in the former. Quenching of HSA by cuminaldehyde was much higher in comparison to that in the presence of cuminol. Fluorescence quenching data were analyzed using modified Stern-Volmer and Lineweaver-Burk methods, which suggested that the binding mechanism was of a static type for both ligands. In both cases, the binding was favored by the domination of hydrophobic as well as hydrogen bonding/Van der Waals forces. Both ligands partially unfolded the secondary structure of HSA, although the effect of cuminaldehyde was more pronounced, as compared to cuminol. The preferred binding site of cuminaldehyde and cuminol inside HSA was also the same; namely, drug binding site 1, located in subdomain IIA. The study showed that cuminaldehyde binds strongly with albumin as compared to its alcohol counterpart, which is due to the more hydrophobic nature of the former.

Keywords: albumin; aldehyde and alcohol; cumin components; cuminol; fluorescence; molecular docking.

Figure 1

(A) UV-visible absorption spectra of cuminaldehyde and cuminol. The concentration of both substances was 40 µM. (B) Different UV-visible spectra of HSA in the absence and presence of cuminaldehyde (0, 40, 80, 120 and 160 µM) and (C) cuminol (0, 100, 200, 300, 500, 700, 1000 and 2000 µM). The concentration of HSA was 3.0 µM at 25 °C.

Figure 2

Fluorescence emission spectra of HSA in the absence and presence of cuminaldehyde at 25 °C (A), 35 °C (B), and 45 °C (C). λ_ex = 295 nm. The concentration of HSA was 3.0 µM, while concentration of cuminaldehyde varied from 0 to 400 µM with a regular increment of 40 µM.

Figure 3

Fluorescence emission spectra of HSA in the absence and presence of cuminol at 25 °C (A), 35 °C (B), and 45 °C (C). λ_ex = 295 nm. The concentration of HSA was 3.0 µM, while concentration of cuminol was 0, 100, 200, 300, 400, 600, 800, 1000, 1500, 2000 µM.

Figure 4

Effect of cuminaldehyde (A) and cuminol (B) on the fluorescence intensities of HSA at λ_ex = 295 nm and 25 °C. [HSA] = 3.0 µM.

Figure 5

Modified Stern-Volmer plots of (A) HSA–cuminaldehyde and (B) HSA–cuminol systems at various temperatures.

Figure 6

Lineweaver-Burk plots of (A) HSA-cuminaldehyde and (B) HSA-cuminol systems at various temperatures.

Figure 7

Van’t Hoff plot for the (A) HSA–cuminaldehyde and (B) HSA–cuminol interactions.

Figure 8

Lineweaver-Burk plots of (A) HSA–cuminaldehyde and (B) HSA–cuminol systems in presence of warfarin or ibuprofen.

Figure 9

Far– UV CD spectra of HSA (3 µM) in absence and presence of (A) cuminaldehyde and (B) cuminol at 25 °C.

Figure 10

(A) Cluster analysis of interaction of cuminaldehyde with HSA (B) binding pocket amino acids (C) 2-D diagram showing the types of interactions involved.

Figure 11

(A) Cluster analysis of interaction of cuminol with HSA (B) binding pocket amino acids (C) 2-D diagram showing the types of interactions involved.