An Improved Methodology for Multidimensional High-Throughput Preformulation Characterization of Protein Conformational Stability

The empirical phase diagram (EPD) technique is a vector-based multidimensional analysis method for summarizing large data sets from a variety of biophysical techniques. It can be used to provide comprehensive preformulation characterization of a macromolecule's higher-order structural integrity and conformational stability. In its most common mode, it represents a type of stimulus-response diagram using environmental variables such as temperature, pH, and ionic strength as the stimulus, with alterations in macromolecular structure being the response. Until now, EPD analysis has not been available in a high-throughput mode because of the large number of experimental techniques and environmental stressor/stabilizer variables typically employed. A new instrument has been developed that combines circular dichroism, ultraviolet absorbance, fluorescence spectroscopy, and light scattering in a single unit with a six-position, temperature-controlled cuvette turret. Using this multifunctional instrument and a new software system, we have generated EPDs for four model proteins. Results confirm the reproducibility of the apparent phase boundaries and protein behavior within the boundaries. This new approach permits two EPDs to be generated per day using only 0.5 mg of protein per EPD. Thus, the new methodology generates reproducible EPDs in high-throughput mode and represents the next step in making such determinations more routine.