Overview of the quantitation of protein interactions

The biological function of many proteins involves reversible interactions with other proteins, nucleic acids, or other non-protein ligands. Such interactions play many different roles in a wide range of cellular processes. A few examples are: (1) storing or transporting key metabolites (e.g., O(2) storage by myoglobin); (2) forming and maintaining the quaternary structure of multi-subunit enzymes; (3) specific binding and recognition events (antigen-antibody, hormone-receptor, transcription factor-promoter); and (4) self-assembly of large structures (microtubules, chromatin). Thus, the quantitative characterization of such interactions represents an important part of understanding the function of such proteins and their role in these cellular events. This unit sets the tone for the rest of the chapter, and gives important information necessary to understand some of the topics that will be covered in future supplements, such as sedimentation equilibrium (analytical and micro-preparative), surface plasmon resonance (SPR), size-exclusion chromatography (SEC) with on-line light scattering, and chemical cross-linking.