Crystal contacts

Crystal contacts are the contacts that occur between molecules in crystals of macromolecules. These contacts are what hold the crystal together. The term crystal contacts is usually used to refer to intermolecular or interchain contacts that occur only in a crystal, and not when the molecule is in its native functional state, and thus are an artifact of crystallization.

In contrast, contacts between chains that occur in the native functional state of the molecule are called specific oligomeric contacts. The resulting functional quaternary structure is called the biological unit or biological assembly. Specific oligomeric contacts occur through interfaces that have co-evolved to fit together and bind under the proper circumstances. Some molecules have multiple quaternary forms. For example, protein phosphorylation often controls the affinities of partner chains for each other.

Crystal contacts tend to be smaller and to involve more hydrophilic surfaces, in contrast to specific oligomeric contacts which are larger and may bury some hydrophobic surface .