Studying effect of homologous protein as impurity on protein crystallization

Homologous protein, which exists in protein solution, is an impurity during protein crystallization. We chose homemade fluorescein isothiocyanate (FITC) labeled hen egg white lysozyme (HEWL) as model homologous lysozyme impurity. We studied the effect of fluorescein isothiocyanate labeled hen egg white lysozyme (FITC-HEWL) on HEWL crystallization. We found that the existence of FITC-HEWL obviously delayed the appearance of HEWL crystals, which indicated that FITC-HEWL changed the nucleation process. At the same time, the amount of final formed HEWL crystals decreased as increase of FITC-HEWL concentration in HEWL crystal growth solution. Moreover, we found that the crystal {110} face growth rate decreased approximately 90% even if only 0.02mg/ml FITC-HEWL existed in HEWL crystal growth solution.