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Adams, P.D., Grosse-Kunstleve, R.W., Hung, L.W., Ioerger, T.R., McCoy, A.J., Moriarty, N.W., Read, R.J., Sacchettini, J.C., Sauter, N.K. and Terwilliger, T.C. (2002) PHENIX, building new software for automated crystallographic structure determination. Acta Crystallographica Section D: Biological Crystallography, 58, 1948-1954. doi:10.1107/S0907444902016657

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• TITLE: Interaction of haptoglobin with hemoglobin octamers based on the mutation αAsn78Cys or βGly83Cys

  AUTHORS: Thomas Brillet, Michael C. Marden, Joanne I. Yeh, Tong-Jian Shen, Nancy T. Ho, Regina Kettering, Shoucheng Du, Corinne Vasseur, Elisa Domingues-Hamdi, Chien Ho, Véronique Baudin-Creuza

  KEYWORDS: Octamers; Hemoglobin; Haptoglobin; Allosteric Transition; Crystallography

  JOURNAL NAME: American Journal of Molecular Biology, Vol.2 No.1, December 30, 2011

  ABSTRACT: Octameric hemoglobins have been developed by the introduction of surface cysteines in either the alpha or beta chain. Originally designed as a blood substitute, we report here the structure and ligand binding function; in addition the interaction with haptoglobin was studied. The recombinant Hbs (rHbs) with mutations alpha Asn78Cys or beta Gly83Cys spontaneously form octamers under conditions where the cysteines are oxidized. Oxygen binding curves and CO kinetic studies indicate a correct allosteric transition of the tetramers within the octamer. Crystallographic studies of the two rHbs show two disulfide bonds per octamer. Reducing agents may provoke dissociation to tetramers, but the octamers are stable when mixed with fresh human plasma, indicating that the reduction by plasma is slower than the oxidation by the dissolved oxygen, consistent with an enhanced stability. The octameric rHbs were also mixed with a solution of haptoglobin (Hp), which binds the dimers of Hb: there was little interaction for incubation times of 15 min; however, on longer timescales a complex was formed. Dynamic light scattering was used to follow the interaction of Hp with the alpha Asn78Cys octamer during 24 hours; a transition from a simple complex of 15 nm to a final size of 60 nm was observed. The results indicate a specific orientation of the αβ dimers may be of importance for the binding to haptoglobin.