Influence of ligand binding on structure and thermostability of human [alpha]1-acid glycoprotein

• Published in: Journal of molecular recognition 2016-02, Vol.29 (2), p.70
• Main Authors: Kopecky, Vladimír, Ettrich, Rudiger, Pazderka, Tomás, Hofbauerova, Katerina, eha, David, Baumruk, Vladimír
• Format: Article
• Language: English
• ISSN: 0952-3499; 1099-1352
• DOI: 10.1002/jmr.2496

Ligand binding of neutral progesterone, basic propranolol, and acidic warfarin to human [alpha]1-acid glycoprotein (AGP) was investigated by Raman spectroscopy. The binding itself is characterized by a uniform conformational shift in which a tryptophan residue is involved. Slight differences corresponding to different contacts of the individual ligands inside the [beta]-barrel are described. Results are compared with in silico ligand docking into the available crystal structure of deglycosylated AGP using quantum/molecular mechanics. Calculated binding energies are -18.2, -14.5, and -11.5kcal/mol for warfarin, propranolol, and progesterone, respectively. These calculations are consistent with Raman difference spectroscopy; nevertheless, minor discrepancies in the precise positions of the ligands point to structural differences between deglycosylated and native AGP. Thermal dynamics of AGP with/without bounded warfarin was followed by Raman spectroscopy in a temperature range of 10-95°C and analyzed by principal component analysis. With increasing temperature, a slight decrease of [alpha]-helical content is observed that coincides with an increase in [beta]-sheet content. Above 45°C, also [beta]-strands tend to unfold, and the observed decrease in [beta]-sheet coincides with an increase of [beta]-turns accompanied by a conformational shift of the nearby disulfide bridge from high-energy trans-gauche-trans to more relaxed gauche-gauche-trans. This major rearrangement in the vicinity of the bridge is not only characterized by unfolding of the [beta]-sheet but also by subsequent ligand release. Hereby, ligand binding alters the protein dynamics, and the more rigid protein-ligand complex shows an improved thermal stability, a finding that contributes to the reported chaperone-like function of AGP. Copyright © 2015 John Wiley & Sons, Ltd.