Crystal structure of Lys beta(1)82-Lys beta(2)82 crosslinked hemoglobin: Apossible allosteric intermediate

The crystal structure of human hemoglobin crosslinked between the Lys beta 82 residues has been determined at 2.30 Angstrom resolution. The crosslinki ng reaction was performed under oxy conditions using bis(3,5-dibromosalicyl ) fumarate; the modified hemoglobin has increased oxygen affinity and lacks cooperativity. Since the crystallization occurred under deoxy conditions, the resulting structure displays conformational characteristics of both the (oxy) R and the (deoxy) T-states. beta 82 chi LHbA does not fully reach it s T-state conformation due to the presence of the crosslink. The R-state-li ke characteristics of deoxy beta 82 chi LHbA include the position of the di stal His beta 63 (E7) residue, indicating a possible reason for the high ox ygen affinity of this derivative. Other areas of the molecule, particularly those thought to be important in the allosteric transition, such as Tyr be ta 145 (HC2) and the switch region involving Pro alpha(1)44 (CD2), Thr alph a(1)41 (C6) and His beta(2)97 (FG4), are in intermediate positions between the R and T-states. Thus, the structure may represent a stabilized intermed iate in the allosteric transition of hemoglobin. (C) 2000 Academic Press.