Contaminant effects on protein crystal morphology in different growth environments

Contaminant effects on the morphology of turkey egg-white lysozyme (TEWL) crystals grown in ungelled and in gelled growth media have been investigated. The latter may serve as a model system for future microgravity experiments. Hen egg-white lysozyme (HEWL) was added as the contaminant at levels ranging from 4 up to 70%(w/w) (total protein). Morphology measurements indicate a contaminant effect leading to a shortening along the c axis of the crystal. This shortening effect depends on the contaminant concentration. It is attenuated and varies more regularly in gelled than in ungelled growth media. The specificity of the HEWL contaminant effect was verified by addition of ribonuclease A, which did not influence crystal morphology. Contaminant inclusion into the growing TEWL crystals could be calculated directly from equilibrium protein concentration measurements. The level of HEWL inclusion is closely related to the concentration of HEWL in the growth solutions. The specificity of the observed effect as well as the differences between the two growth media are discussed.