The 2,3-BPG binding pocket of deoxyHb A "collapses" in the conformational shift to oxyHb A.   Hb A Structure Overview

The amino acid residues forming the 2,3-BPG (BPG) binding pocket of deoxyHb A (left) are symmetrically positioned along the surface of the β1 and β2 subunit interface. 8 of these residues, 4 from each β-subunir, have positively charged ionizable groups that form salt briges with the negatively charged phosphate and carboxyl groups of bound BGP (which is physically absent from this deoxyHb A structure). These positively charged groups include the α-amino groups of both β-Val 1 residues; the ε-amino groups of both β-Lys 82 residues; and the imidazole sidechain groups of both β-His 2 and both β-His 143 residues. These groups can be highlighted with the "Spacefill/Zoom' and "Wireframe/Zoom" buttons below and then labeled with the "Charge distribution" and "Charged AA resdiues" checkboxes.

In the oxyHb A conformation (right), these residues are spatially reorganized so that the pocket "collapses" and BPG is no longer able to bind. Thus, BPG and O₂ dynamically regulate the transport and delivery of O₂ in the blood in the following way. When O₂ levels are higher, O₂ binding stabilizes oxyHb A causing the release of bound BPG as hemoglobin switches to this higher affinity conformation. In contrast, when O₂ levels are lower, BPG binding to deoxyHb A is favored causing the release of bound O₂ as hemoglobin switches to this lower affinity conformation.

© Duane W. Sears
Revised: August 1, 2015
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