RAPID COMMUNICATION Comparative Signature Diagrams to Evaluate Biophysical Data for Differences in Protein Structure Across Various Formulations

A solution to the problem of being able to show statistically significant dif- ferences in the measurements of various levels of higher-order protein structure has been an elusive one. We propose the use of comparative signature diagrams (CSDs) to this end. CSDs compare datasets from different biophysical techniques that fingerprint the secondary, tertiary, and quaternary structures of a protein molecule and display statistically significant differences in these datasets. In this paper, we explore the differences in the structures of two proteins (Granulocyte Colony Stimulating Factor (GCSF) and a monoclonal antibody (mAb)) in various formulations. These proteins were chosen based on the extent of differences in struc- ture observed in the formulations. As an initial test, we utilize data from circular dichroism, 8-anilino-1-naphthalene-sulfonate and intrinsic fluorescence spectroscopy, and static light scat- tering measurements to fingerprint protein structure in the different formulations. Several layers of statistics were explored to visualize the regions of significant differences in the protein spectra. This approach provides a rapid, high-resolution methodology to compare various struc- tural levels of proteins using standard biophysical instrumentation. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:43-51, 2013