A low energy short hydrogen bond in very high resolution structures of protein receptor--phosphate complexes

A very short hydrogen bond between an Asp and a phosphate is established in two high resolution structures (0.98 and 1.05 A). A mutant complex that changes the Asp to an Asn, which forms a normal hydrogen bond, has a similar free energy of binding to the wild type complex, suggesting that the contribution of the short hydrogen bond is not extraordinarily strong.