Inorganic Stabilisation of the Active Form: The H2O Lock

In addition to stabilisation of the adrenoceptor active state by the engineered NbSB9 antibody and the substrate, another force involved in rendering the active form energetically favourable is the formation of a hydrogen bond between tyr219 and tyr326 (Ring et al., 2013). This bond is shown below:

The hydrogen bond to the water molecule (marine blue) pulls together the two tyrosine residues (cyan)  and thus helps hold together the transmembrane domain characterising the adrenoceptor active state.