title: Influence of ligand binding on structure and thermostability of human α1-acid glycoprotein.
abstract: Ligand binding of neutral progesterone, basic propranolol, and acidic warfarin to human α1-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 β-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 -11.5 kcal/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 α-helical content is observed that coincides with an increase in β-sheet content. Above 45 °C, also β-strands tend to unfold, and the observed decrease in β-sheet coincides with an increase of β-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 β-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.
authors.affiliation: Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116, Prague 2, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Kopecký
authors.affiliation: Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zámek 136, CZ-37333, Nové Hrady, Czech Republic.|Faculty of Sciences, University of South Bohemia, Zámek 136, CZ-37333, Nové Hrady, Czech Republic.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Ettrich
authors.affiliation: Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116, Prague 2, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Pazderka
authors.affiliation: Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116, Prague 2, Czech Republic.|Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-142 20, Prague 4, Czech Republic.
authors.forename: Kateřina
authors.initials: K
authors.lastname: Hofbauerová
authors.affiliation: Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zámek 136, CZ-37333, Nové Hrady, Czech Republic.|Faculty of Sciences, University of South Bohemia, Zámek 136, CZ-37333, Nové Hrady, Czech Republic.
authors.forename: David
authors.initials: D
authors.lastname: Řeha
authors.affiliation: Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116, Prague 2, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Baumruk
mesh_terms: D001665:Binding Sites; D006801:Humans; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D009961:Orosomucoid / Q000737:chemistry* / Q000378:metabolism*; D011374:Progesterone / Q000737:chemistry / Q000378:metabolism*; D011433:Propranolol / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics; D014364:Tryptophan / Q000378:metabolism; D014859:Warfarin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009961:Orosomucoid; D011374:Progesterone; D014859:Warfarin; D014364:Tryptophan; D011433:Propranolol
keywords: Raman spectroscopy; binding site; molecular modeling; orosomucoid; thermal stability