Chapter 7 Tools to Enhance Membrane Protein Crystallization

Abstract

Publisher Summary This chapter describes a novel technique, self-interaction chromatography (SIC), to rapidly measure the second virial coefficient, B, (a thermodynamic term that provides semiquantitative information regarding protein–protein interactions) of proteins in a variety of cosolvents. SIC provides a rapid diagnostic for determining the optimum solution conditions that promote increased protein stability and minimize unwanted nonspecific aggregation. In addition, SIC allows the selection of specific solution conditions (including detergent type and concentration) for subsequent optimization of protein solubility, homogeneity, and crystallization. Balanced solubility and crystallization screens have been designed, such that B values are experimentally measured via SIC for a relatively small number of conditions, providing a balanced representation of the total number of possible combinations of chemical variables. The screen conditions plus corresponding B values are then used to train a predictive algorithm (neural net) that subsequently produces an in silico screen, predicting the B values for all possible combinations of the chemical variables. The high-positive B values indicate solution conditions that should provide increased protein solubility and consequently, minimization of nonspecific protein aggregation. Slightly negative B values indicate solution conditions that have a higher probability of yielding crystals. The combined use of these innovative technologies provides a powerful approach to address several of the critical impediments (i.e., protein production, stability, purification, and crystallization) preventing membrane structure determinations.