The structure of water clusters (H(2)O)(n) (n = 40-200) and bulk water were examined by molecular dynamics simulations using the TIP4P-ice water model. The analysis of the low-temperature structures in terms of the local structure index (LSI) showed a bimodal distribution. This finding supports the two-state picture derived from the analysis of the inherent dynamics of bulk SPC/E water. The water molecules at the outer interface of the coldest clusters are more structured than those in the inner core. The geometrical constraint of the interface forces the surface molecules to lose one neighbor and adopt a local angular distribution of hydrogen bonds resembling that found in the basal plane of ice Ih.

Allosteric modulators of kinase function are of considerable pharmacological interest as blockers or agonists of key cell-signaling pathways. They are gaining attention due to their purported higher selectivity and efficacy relative to ATP-competitive ligands. Upon binding to the target protein, allosteric inhibitors promote a conformational change that purposely facilitates or hampers ATP binding. However, allosteric binding remains a matter of contention because the binding site does not fit with a natural ligand (i.e. ATP or phosphorylation substrate) of the protein. In this study, we show that allosteric binding occurs by means of a local structural motif that promotes association with the ligand. We specifically show that allosteric modulators promote a local metastable state that is stabilized upon association. The induced conformational change generates a local enrichment of the protein in the so-called dehydrons, which are solvent-exposed backbone hydrogen bonds. These structural deficiencies that are inherently sticky are not present in the apo form and constitute a local metastable state that promotes association with the ligand. This productive induced metastability (PIM) is likely to translate into a general molecular design concept.