Porcine HpHb complex

There are in total 57 residues contributes to the irreversible binding of the haptoglobin and haemoglobin. The interaction is irreversible in vivo which contributes to prevention of free radical of haem group forming when haemoglobins are released by ruptured red blood cells (Andersen et al., 2012).

Figure 5. Summary of all the interactions between residues of haptoglobin (shown in blue) and alpha and beta subunits of haemoglobin (shown in orange). Van Der Waal’s interactions are shown as grey line. Hydrogen bonds are shown as dashed black lines. Salt bridges are shown as black lines. 

Movie 1: All the interaction between Hp and Hb involving van der waal’s interactions, salt bridges and hydrogen bonds shows in yellow dashed lines. The interaction takes place between haptoglobin serine protease domain (in pink) and haemoglobin alpha (in blue) and beta (in green) subunits. All the residues involved are labelled and shown as lines.

Some residues in haemoglobin are especially prone to oxidative damage (Figure 6) Tyrosine 42 is thought to be involved in movement of free radicals from one haemoglobin chain to the other. Many of them are located on the binding surface between Hb and Hp so that it is likely that binding of Hp shields those residues against free radical formation (Andersen et al., 2012). 

Figure 6: Hb residues especially susceptible to free radical damage shown in red.