Allosteric transition intermediates modelled by crosslinked haemoglobins.
The structural end-points of haemoglobin's transition from its low-oxygen-affinity (T) to high-oxygen-affinity (R) state, have been well established by X-ray crystallography, but short-lived intermediates have proved less amenable to X-ray studies. Here we use chemical crosslinking to fix these intermediates for structural characterization. We describe the X-ray structures of three haemoglobins, alpha 2 beta 1S82 beta, alpha 2 beta 1Tm82 beta and alpha 2 beta 1,82Tm82 beta, which were crosslinked between the amino groups of residues beta Val1 and beta Lys82 by 3,3'-stilbenedicarboxylic acid (S) or trimesic acid (Tm) while in the deoxy state, and saturated with carbon monoxide before crystallization. alpha 2 beta 1S82 beta, which has almost normal oxygen affinity, is completely in the R-state conformation; however, alpha 2 beta 1Tm82 beta and alpha 2 beta 1,82Tm82 beta, both of which have low oxygen affinity, have been prevented from completing their transition into the R state and display many features of a transitional intermediate. These haemoglobins therefore represent a snapshot of the nascent R state.
Schumacher
M A
MA
Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098, USA.
Dixon
M M
MM
Kluger
R
R
Jones
R T
RT
Brennan
R G
RG
D000494:Allosteric Regulation; D003196:Computer Graphics; D003432:Cross-Linking Reagents; D018360:Crystallography, X-Ray; D006454:Hemoglobins / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation
D003432:Cross-Linking Reagents; D006454:Hemoglobins; D010100:Oxygen