Illuminating protein crystal growth using fluorophore-labelled proteins

Incorporation of trace amounts of fluorophore-labelled proteins is used to study several optical properties and the growth history of protein crystals. Qualitative characterisations of the crystals have been performed by means of confocal laser scanning microscopy and polarisation microscopy. Our results first of all show that labelled proteins do not always act as micro-heterogeneous impurities for the crystals of their parent proteins and may behave differently towards different polymorphs of these protein crystals. Furthermore, labelled proteins may also show a distribution profile very different from their unlabelled counterparts when added as a heterogeneous impurity during crystallisation. Nevertheless, a labelled protein that is incorporated in the growing crystals of its unlabelled counterpart can already provide valuable qualitative information on crystal symmetry and growth history, based upon its orientation, distribution and incorporation efficiency into the host crystals.