Protein crystallization: magical or logical: can we establish some general rules?

Abstract

The systematic-type studies carried out on small molecule crystallization are of limited use when dealing with proteins. The reasons for this are that proteins have a much higher molecular weight, typically ranging from 10000 to 250000 daltons and are of lower symmetry than small molecules. Protein crystals are 'soft' and sensitive to small changes in external conditions since they have a high solvent content. There are small binding energies between protein molecules in the crystal lattice. This means that there are a large number of potential attachment sites which are almost as favourable as the small number of specific sites through which the ordered array is formed. Despite these problems, some general rules have been established and procedures devised that can be followed when attempting to crystallize a new protein. These rules and procedures are illustrated by using specific examples of crystals grown from monomeric and multisubunit proteins isolated from a variety of bacterial and animal sources.