Phase Diagram Visualization via Continuously-Fed Crystallization: Experiments and Model

Abstract

A protein’s atomic level three-dimensional structure is typically determined by X-ray diffraction of a high-quality protein crystal (Figure 1a). The X-ray bream is diffracted inside the crystal producing spots at various locations (Figure 1b) which can be used to back out the location of the electron cloud of the protein which is used to solve the structure (Figure 1c). The current bottleneck in these structural determination projects is in growing a diffraction quality protein crystal. Current growth methods involve testing hundreds of conditions in this multi-parametric process without knowledge of the protein phase diagram (PD). In this work, a microfluidic crystallization chamber is manufactured to allow phase diagram visualization to predict the PD of a protein in a single experiment. This phase diagram visualizer (PDV) screens a large range of protein and salt concentrations by controlling the transport mechanism (convection and diffusion) of both salt and protein. The PDV has been fabricated and its flow and concentration profiles have been determined using a computational model. The PDV has predicted the metastable line of the phase diagram for tetragonal lysozyme (known PD) and the solubility line for triclinic lysozyme (unknown PD).