Development of Fluorescence Label and Con-focal Laser Scanning Microscopy Method for Non-Destructive Local Impurity Distribution Analysis in Protein Crystals

Abstract

A new method for quantitative analysis of the impurity concentration in protein crystals and solutions was developed. This technique utilizes fluorescence label (FL) with con-focal laser scanning microscopy (CLSM), which is more effective than SDS-PAGE analysis currently used for this purpose. The advantages of CLSM are that, it is non-destructive so that the impurity incorporation and local distribution could be observed in situ, and also that only a micro-quantity of protein solution is needed. The impurity protein is labeled with fluorescence material, and mixed with the crystallization solution. The solution and the crystal are observed by CLSM, and the fluorescence intensity from the labeled impurity is then converted to the impurity concentration by using calibration curves. A case study using Hen Egg White Lysozyme as a sample is reported. Calibration curves were obtained by comparing the fluorescence intensity and the actual impurity concentration determined by the absorbance at 280 nm and SDS-PAGE. A few factors such as the numerical aperture of the objective lens or the pinhole size were fixed. The utilization of this technique leads to the understanding of the effect of impurities on protein crystal growth.