Abstract
Our goal was to design a single hemoglobin subunit able to assemble into a stable tetrameric structure with cooperative O2 binding and low oxygen affinity. We have synthesized in E. coli a chimeric beta/alpha globin subunit composed of the first 73 residues of the beta chain and the last 73 residues of the alpha chain. Molecular building indicated that this construction could result in Hb homotetramers possessing the alpha 1 beta 2 interface, responsible for the heme-heme interaction in Hb heterotetramers. The results show that the chimeric subunits assemble into tetramers which bind oxygen reversibly without cooperativity but with an oxygen affinity slightly lower than observed for human Hb. The strong effector RSR 4 lowers the oxygen affinity. Kinetics of CO recombination in the presence of RSR 4 reveal a biphasic bimolecular rebinding. Functional studies suggest that the quaternary structure of the oligomer is intermediary between R-and T-state.
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