Interaction among subunits: salt bridges in deoxyhaemoglobin

Both the structure of each subunit in deoxyhaemoglobin (tertiary structure) and the interaction among the four subunits (quaternary structure) are stabilised by 8 salt bridges (electrostatic interactions), formed between sidechains from several amino acids and the terminal carboxy and amino groups of the alpha chains:


Salt bridges between the two alpha chains

The terminal amino group in one alpha chain, Val1, forms a salt bridge with the terminal carboxy group in the other alpha chain, Arg141 .

In addition, the guanidinium group (sidechain) of the same Arg141 forms a salt bridge with the carboxy group in the sidechain of Asp126 from the other alpha chain.

Each type of amino acid in a colour (Val, Asp, Arg)

To see the interactions in detail, let's the model
(α1Val1 :: α2Arg141 :: α1Asp126)
highlight the atoms in the salt bridge (always N+ group with O group)

Salt bridges in beta chains

The terminal carboxy group in one beta chain, His146, forms a salt bridge with the amino group in the sidechain of Lys40 from an alpha chain (β1His146 :: α2Lys40 y β2His146 :: α1Lys40).

In addition, the same His146 forms another salt bridge, by its sidechain, with the carboxy group in the sidechain of Asp94 from its same beta chain. Differently to all the former ones, this is an intrachain bridge.

Each type of amino acid in a colour (His, Asp, Lys)

To see the interactions in detail, let's the model
(α2Lys40 :: β1His146 :: β1Asp94)
highlight the atoms in the salt bridge (always N+ group with O group)

Detail of this salt bridge:


To end, the whole deoxyhaemoglobin molecule with its 8 salt bridges.