TY - JOUR
T1 - The unique heme-heme interactions of the homodimeric Scapharca inaequivalvis hemoglobin as probed in the protein reconstituted with unnatural 2,4 heme derivatives
AU - Zamparelli, Carlotta
AU - Verzili, Daniela
AU - Boffi, Alberto
AU - Chiancone, Emilia
AU - Takahashi, Satoshi
AU - Rousseau, Denis L.
AU - Regan, Rebecca
AU - Gibson, Quentin H.
N1 - Funding Information:
1Grants from the Ministero dell'UniversitaÁ e Ricerca Scienti®ca 40 and 60% to E. Chiancone and Grant GM 48714 from the National Institute of General Medical Sciences to D. L. Rousseau are gratefully acknowledged.
PY - 1997/3/15
Y1 - 1997/3/15
N2 - In the homodimeric hemoglobin from Scapharca, HbI, functional communication between the two heme groups is based on their direct structural linkage across the subunit interface through the heme propionates. The heme- protein interactions have been altered in deutero- and meso-HbI by substituting the vinyl groups at positions 2 and 4 of protoheme with hydrogen and ethyl groups, respectively. In meso-HbI the introduction of the ethyl groups in the heme pocket induces significant alterations in the conformation of the heme peripheral substituents, including the propionates, and in the structure of bound CO, as revealed by the resonance Raman spectra. The functional counterpart of these structural changes is the loss of cooperativity in carbon monoxide binding and in the rate of oxygen dissociation. Oxygen pulse and flash photolysis experiments indicate that meso-HbI is locked in the liganded conformation. It is postulated that the ethyl groups, which occupy a larger volume than vinyl ones, impair the ligand-linked movement of the heme relative to its pocket and in turn the expression of cooperativity. In deutero-HbI structural alterations have not been monitored. Functionally, cooperativity in the CO binding kinetics is increased as if hydrogen atoms at positions 2 and 4 permitted more marked movements of the heme than in the native protein.
AB - In the homodimeric hemoglobin from Scapharca, HbI, functional communication between the two heme groups is based on their direct structural linkage across the subunit interface through the heme propionates. The heme- protein interactions have been altered in deutero- and meso-HbI by substituting the vinyl groups at positions 2 and 4 of protoheme with hydrogen and ethyl groups, respectively. In meso-HbI the introduction of the ethyl groups in the heme pocket induces significant alterations in the conformation of the heme peripheral substituents, including the propionates, and in the structure of bound CO, as revealed by the resonance Raman spectra. The functional counterpart of these structural changes is the loss of cooperativity in carbon monoxide binding and in the rate of oxygen dissociation. Oxygen pulse and flash photolysis experiments indicate that meso-HbI is locked in the liganded conformation. It is postulated that the ethyl groups, which occupy a larger volume than vinyl ones, impair the ligand-linked movement of the heme relative to its pocket and in turn the expression of cooperativity. In deutero-HbI structural alterations have not been monitored. Functionally, cooperativity in the CO binding kinetics is increased as if hydrogen atoms at positions 2 and 4 permitted more marked movements of the heme than in the native protein.
KW - cooperativity
KW - dimeric hemoglobin (Scapharca)
KW - unnatural heme derivatives
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U2 - 10.1006/abbi.1996.9829
DO - 10.1006/abbi.1996.9829
M3 - Article
C2 - 9056259
AN - SCOPUS:0031569380
SN - 0003-9861
VL - 339
SP - 275
EP - 282
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 2
ER -