Binding sites of retinol and retinoic acid with serum albumins

• Published in: European journal of medicinal chemistry Vol. 48; pp. 114 - 123
• Main Authors: Belatik, A., Hotchandani, S., Bariyanga, J., Tajmir-Riahi, H.A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Masson SAS 01-02-2012; Elsevier
• Subjects: Animals; Binding Sites; Biological and medical sciences; Biological Transport; BSA; Cattle; Circular Dichroism; Fundamental and applied biological sciences. Psychology; HSA; Intermolecular phenomena; Kinetics; Miscellaneous; Modeling; Models, Molecular; Molecular biophysics; Molecular Dynamics Simulation; Protein Binding; Retinoid; Serum Albumin, Bovine - chemistry; Serum Albumin, Bovine - metabolism; Spectrometry, Fluorescence; Spectroscopy; Spectroscopy, Fourier Transform Infrared; Surface Properties; Tretinoin - chemistry; Tretinoin - metabolism; Vitamin A - chemistry; Vitamin A - metabolism; ret; BSA; Spectroscopy; CD; retac; FTIR; Retinoid; HSA; Modeling; Physiological condition; Fourier transformation; Binding site; Serum albumin; Serum protein; Secondary structure; Fluorescence spectrometry; Retinol; Infrared spectrometry; Circular dichroism spectrometry; Molecular model; Aqueous solution; Retinoic acid
• ISSN: 0223-5234; 1768-3254
• DOI: 10.1016/j.ejmech.2011.12.002

Retinoids are effectively transported in the bloodstream
via serum albumins. We report the complexation of bovine serum albumin (BSA) with retinol and retinoic acid at physiological conditions, using constant protein concentration and various retinoid contents. FTIR, CD and fluorescence spectroscopic methods and molecular modeling were used to analyze retinoid binding site, the binding constant and the effects of complexation on BSA stability and secondary structure. Structural analysis showed that retinoids bind BSA
via hydrophilic and hydrophobic interactions with overall binding constants of
K
Ret
–BSA = 5.3 (±0.8) × 10
6 M
−1 and
K
Retac
–BSA = 2.3 (±0.4) × 10
6 M
−1. The number of bound retinoid molecules (
n) was 1.20 (±0.2) for retinol and 1.8 (±0.3) for retinoic acid. Molecular modeling showed the participation of several amino acids in retinoid–BSA complexes stabilized by H-bonding network. The retinoid binding altered BSA conformation with a major reduction of α-helix from 61% (free BSA) to 36% (retinol–BSA) and 26% (retinoic acid–BSA) with an increase in turn and random coil structures indicating a partial protein unfolding. The results indicate that serum albumins are capable of transporting retinoids
in vitro and
in vivo.
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► The binding sites of retinol and retinoic acid were located on BSA and HSA. ► Retinoids bind serum albumins
via several amino acids with hydrophobic and hydrophilic contacts. ► Stronger complexes formed with BSA leading to protein destabilization. ► The results support the effective transportation of retinoids
via serum albumins
in vitro. ► Strong acid-BSA binding reduces the isomerization of
cis-retinoic acid to
trans-retinoic acid.