Measurement and analysis of equilibrium binding titrations: A beginner's guide

Binding events are central to biology. Simple binding of a substrate to an enzyme initiates catalysis. Formation of protein:protein complexes is integral to signal transduction. Binding of multiple proteins to the ribosomal ribonucleic acid (rRNA) results in ribosome assembly. Consequently, elucidation of mechanisms of biological processes requires binding measurements. Such measurements reveal, among other things, the relevant concentrations required for binding partners to form a complex and are indispensible to understanding the relationship between structure and biological function. This article is intended to serve as a primer for biologists who are contemplating performing binding studies. The focus is on practical aspects of design and analysis of binding measurements for a simple process. The information that one can extract from such measurements is also addressed. Theoretical background on binding for both simple and complex systems can be found in many textbooks and monographs including those by Hammes [Hammes, G. G. (2000). Thermodynamics and Kinetics for the Biological Sciences. Wiley, New York, NY], Weber [Weber, G. (1992). Protein Interactions. Chapman and Hall, New York, NY], and Wyman and Gill [Wyman, J. and Gill, S. J. (1990). Binding and Linkage. University Science Books, Mill Valley, CA]. While the first reference is excellent for beginners, the latter two, in addition to discussion of simple binding, contain theoretical background for complex binding processes.