TY - JOUR
T1 - Ibuprofen induces an allosteric conformational transition in the heme complex of human serum albumin with significant effects on heme ligation
AU - Nicoletti, Francesco P.
AU - Howes, Barry D.
AU - Fittipaldi, Maria
AU - Fanali, Gabriella
AU - Fasano, Mauro
AU - Ascenzi, Paolo
AU - Smulevich, Giulietta
PY - 2008/9/3
Y1 - 2008/9/3
N2 - Human serum albumin (HSA), the most prominent protein in blood plasma, is able to bind a wide range of endogenous and exogenous compounds. Among the endogenous ligands, HSA is a significant transporter of heme, the heme-HSA complex being present in blood plasma. Drug binding to heme-HSA affects allosterically the heme affinity for HSA and vice versa. Heme-HSA, heme, and their complexes with ibuprofen have been characterized by electronic absorption, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopy. Comparison of the results for the heme and heme-HSA systems has provided insight into the structural consequences on the heme pocket of ibuprofen binding. The pentacoordinate tyrosine-bound heme coordination of heme-HSA, observed in the absence of ibuprofen, becomes hexacoordinate low spin upon ibuprofen binding, and heme dissociates at increasing drug levels. The electronic absorption spectrum and ν(Fe-CO)/ν(CO) vibrational frequencies of the CO-heme-HSA-ibuprofen complex, together with the observation of a Fe-His Raman mode at 218 cm-1 upon photolysis of the CO complex and the low spin EPR g values indicate that a His residue is one of the low spin axial ligands, the sixth ligand probably being Tyr161. The only His residue in the vicinity of the heme Fe atom is His146, 9 Å distant in the absence of the drug. This indicates that drug binding to heme-HSA results in a significant rearrangement of the heme pocket, implying that the conformational adaptability of HSA involves more than the immediate vicinity of the drug binding site. As a whole, the present spectroscopic investigation supports the notion that HSA could be considered as the prototype of monomeric allosteric proteins.
AB - Human serum albumin (HSA), the most prominent protein in blood plasma, is able to bind a wide range of endogenous and exogenous compounds. Among the endogenous ligands, HSA is a significant transporter of heme, the heme-HSA complex being present in blood plasma. Drug binding to heme-HSA affects allosterically the heme affinity for HSA and vice versa. Heme-HSA, heme, and their complexes with ibuprofen have been characterized by electronic absorption, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopy. Comparison of the results for the heme and heme-HSA systems has provided insight into the structural consequences on the heme pocket of ibuprofen binding. The pentacoordinate tyrosine-bound heme coordination of heme-HSA, observed in the absence of ibuprofen, becomes hexacoordinate low spin upon ibuprofen binding, and heme dissociates at increasing drug levels. The electronic absorption spectrum and ν(Fe-CO)/ν(CO) vibrational frequencies of the CO-heme-HSA-ibuprofen complex, together with the observation of a Fe-His Raman mode at 218 cm-1 upon photolysis of the CO complex and the low spin EPR g values indicate that a His residue is one of the low spin axial ligands, the sixth ligand probably being Tyr161. The only His residue in the vicinity of the heme Fe atom is His146, 9 Å distant in the absence of the drug. This indicates that drug binding to heme-HSA results in a significant rearrangement of the heme pocket, implying that the conformational adaptability of HSA involves more than the immediate vicinity of the drug binding site. As a whole, the present spectroscopic investigation supports the notion that HSA could be considered as the prototype of monomeric allosteric proteins.
UR - http://www.scopus.com/inward/record.url?scp=51349131362&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=51349131362&partnerID=8YFLogxK
U2 - 10.1021/ja800966t
DO - 10.1021/ja800966t
M3 - Article
C2 - 18681435
AN - SCOPUS:51349131362
VL - 130
SP - 11677
EP - 11688
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 35
ER -