Crystal forms of avidin

This chapter describes various types of crystal forms of Avidin. The first single crystal forms of egg-white Avidin were obtained using the dialysis method at room temperature by equilibrating a solution containing 10–20 mg/ml of protein versus a sodium phosphate buffer at pH 5.2. Crystals appeared when the buffer concentration was increased to about 3.0 M. A different crystal form was obtained from polyethylene glycol (PEG) 6000. These crystals were grown using the batch method 3 at room temperature. The protein solution contained 20–45 mg/ml protein, 10 mM sodium phosphate (pH 6.0), and 150 mM NaCI. The carbohydrate moiety of the avidin is not essential for its biotin-binding activity. The biotin-binding properties of the nonglycosylated avidin are equivalent to those obtained for the native (glycosylated) avidin molecule. The method consists of first coating the crystal with viscous oil in the crystallization droplet and removing all traces of mother liquor. The crystal is then picked up with a thin glass spatula, putting it directly under a stream of boiled liquid N₂ at a temperature of approximately 90 K.