Tertiary structure of human alpha1-acid glycoprotein (orosomucoid). Straightforward fluorescence experiments revealing the presence of a binding pocket.
Binding of hemin to alpha1-acid glycoprotein has been investigated. Hemin binds to the hydrophobic pocket of hemoproteins. The fluorescent probe 2-(p-toluidino)-6-naphthalenesulfonate (TNS) binds to a hydrophobic domain in alpha1-acid glycoprotein with a dissociation constant equal to 60 microM. Addition of hemin to an alpha1-acid glycoprotein-TNS complex induces the displacement of TNS from its binding site. At saturation (1 hemin for 1 protein) all the TNS has been displaced from its binding site. The dissociation constant of hemin-alpha1-acid glycoprotein was found equal to 2 microM. Thus, TNS and hemin bind to the same hydrophobic site: the pocket of alpha1-acid glycoprotein. Energy-transfer studies performed between the Trp residues of alpha1-acid glycoprotein and hemin indicated that efficiency (E) of Trp fluorescence quenching was equal to 80% and the Förster distance, R0 at which the efficiency of energy transfer is 50% was calculated to be 26 A, revealing a very high energy transfer.
Albani
Jihad R
JR
Laboratoire de Biophysique Moléculaire, Université des Sciences et Technologies de Lille, Bâtiment C6, 59655, Villeneuve d'Ascq Cedex, France. jihad-rene.albani@univ.lille1.fr
D001665:Binding Sites; D005453:Fluorescence; D006427:Hemin / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D009961:Orosomucoid / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D017186:Titrimetry
D009961:Orosomucoid; D006427:Hemin