Haemoglobin: the surface buried between the alpha 1 beta 1 and alpha 2 beta 2 dimers in the deoxy and oxy structures

Using the newly available refined co-ordinates of deoxy and oxyhaemoglobin, we have re-examined and compared the interfaces between the dimers alpha 1 beta 1 and alpha 2 beta 2. The most extensive monomer-monomer contacts are between alpha 1 and beta 2, and, symmetrically, alpha 2 and beta 1. In oxyhaemoglobin these interfaces bury 700 A2 less protein surface than in deoxyhaemoglobin. The alpha 1 alpha 2 interface involves similar salt bridges in both forms, but in oxyhaemoglobin buries 240 A2 more surface than in deoxyhaemoglobin. There is a loosely packed beta 1 beta 2 interface burying 320 A2 of surface in oxyhaemoglobin; there is no beta 1 beta 2 interface in deoxyhaemoglobin. The greater stability of the deoxy form, in the absence of ligands, can be attributed to a combination of hydrophobic, van der Waals' and electrostatic interactions.