Loss of allosteric behaviour in recombinant hemoglobin alpha 2 beta 2(92)(F8) His-->Ala: restoration upon addition of strong effectors.
In the stereochemical model proposed by Perutz [1], the Fe-His(F8) bond plays a significant role in the allosteric transition in hemoglobin and the resulting cooperativity in ligand binding. When this bond is ruptured, there is a loss in the transmission of the information concerning ligand binding; examples are Hb(NO)4 in the presence of inositol hexakisphosphate (IHP), or nickel substituted Hb hybrids which, despite being liganded, exhibit deoxy-like properties. To study the effects of the loss of the iron proximal histidine bond, we have engineered the alpha 2 beta 2(F8)H92A recombinant Hb. The replacement of the highly conserved proximal histidine F8 residue by an alanine results in a low affinity for the heme group and a loss of the allosteric properties; kinetics of CO recombination after photodissociation show only the rapid bimolecular phase, characteristic of the high affinity R-state. However, a significant amount of deoxy (T-state) kinetics are observed after addition of external effectors such as IHP. The iron-histidine bond is apparently crucial for the heme-heme interaction, but the allosteric equilibrium may still be influenced by external constraints.
Dumoulin
A
A
Institut National de la Santé et de la Recherche Médicale U 299, Hôpital de Bicêtre, France.
Kiger
L
L
Jiang
R
R
Baudin
V
V
Vasseur
C
C
Sligar
S G
SG
Marden
M C
MC
Pagnier
J
J
Poyart
C
C
D000409:Alanine / Q000737:chemistry; D000495:Allosteric Site / Q000187:drug effects; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics; D006639:Histidine / Q000737:chemistry; D007093:Imidazoles / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D010671:Phenylurea Compounds / Q000494:pharmacology; D010833:Phytic Acid / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000737:chemistry
D006454:Hemoglobins; D007093:Imidazoles; D010671:Phenylurea Compounds; D011993:Recombinant Fusion Proteins; C064071:L 345; D006639:Histidine; D010833:Phytic Acid; D000409:Alanine