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. 2020 Mar 6;21(5):1823.
doi: 10.3390/ijms21051823.

Interaction of the Coffee Diterpenes Cafestol and 16- O-Methyl-Cafestol Palmitates with Serum Albumins

Federico Berti  1 , Luciano Navarini  2 , Elena Guercia  2 , Ana Oreški  1 , Alessandra Gasparini  1 , Jeremy Scoltock  1 , Cristina Forzato  1
Affiliations

Interaction of the Coffee Diterpenes Cafestol and 16- O-Methyl-Cafestol Palmitates with Serum Albumins

Federico Berti et al. Int J Mol Sci. .

Abstract

The main coffee diterpenes cafestol, kahweol, and 16-O-methylcafestol, present in the bean lipid fraction, are mostly esterified with fatty acids. They are believed to induce dyslipidaemia and hypercholesterolemia when taken with certain types of coffee brews. The study of their binding to serum albumins could help explain their interactions with biologically active xenobiotics. We investigated the interactions occurring between cafestol and 16-O-methylcafestol palmitates with Bovine Serum Albumin (BSA), Human Serum Albumin (HSA), and Fatty Free Human Serum Albumin (ffHSA) by means of circular dichroism and fluorimetry. Circular Dichroism (CD) revealed a slight change (up to 3%) in the secondary structure of fatty-free human albumin in the presence of the diterpene esters, suggesting that the aliphatic chain of the palmitate partly occupies one of the fatty acid sites of the protein. A warfarin displacement experiment was performed to identify the binding site, which is probably close but not coincident with Sudlow site I, as the affinity for warfarin is enhanced. Fluorescence quenching titrations revealed a complex behaviour, with Stern-Volmer constants in the order of 103-104 Lmol-1. A model of the HSA-warfarin-cafestol palmitate complex was obtained by docking, and the most favourable solution was found with the terpene palmitate chain inside the FA4 fatty acid site and the cafestol moiety fronting warfarin at the interface with site I.

Keywords: circular dichroism; coffee; diterpenes; fluorescence; serum albumin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Structure of diterpenes and diterpene palmitates
Figure 2
Figure 2
Domains of HSA (left) and map of its binding sites (right).
Figure 3
Figure 3
Circular dichroism spectra of 5 μM ffHSA albumin (black) and upon addition of 2 (red) and 4 (green) at 100 µM concentration.
Figure 4
Figure 4
Fluorescence emission of warfarin (excitation 320 nm, emission 380 nm) in the presence of 1 μM albumin and increasing concentrations of 2 (A) and 4 (B).
Figure 5
Figure 5
Emission spectra of 1 μM BSA (A and B), HSA (C and D) and ffHSA (E and F) upon addition of increasing amounts of 2 and 4. The final concentrations of diterpene were 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450 and 500 μM.
Figure 5
Figure 5
Emission spectra of 1 μM BSA (A and B), HSA (C and D) and ffHSA (E and F) upon addition of increasing amounts of 2 and 4. The final concentrations of diterpene were 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450 and 500 μM.
Figure 6
Figure 6
Stern–Volmer plots. (A): BSA emission at 340 nm upon addition of 2 (black) and 4 (white). (B): HSA emission at 330 nm upon addition of 2 (black) and 4 (white). (C): ffHSA emission at 335 (black) and 310 nm (white) upon addition of 2. (D): ffHSA emission at 335 (black) and 310 nm (white) upon addition of 4.
Figure 7
Figure 7
Best docking solution for cafestol palmitate (CP) inside FA4-Sudlow I sites.
See this image and copyright information in PMC

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