Using charge ladders and capillary electrophoresis to measure the charge, size, and electrostatic interactions of proteins.

This chapter provides an overview of protein charge ladders--collections of protein derivatives that differ in charge--and capillary electrophoresis (CE). The combination of charge ladders and CE is a useful biophysical tool for measuring the net charge of proteins and the role of electrostatics in biochemical processes involving proteins. Methods to synthesize and analyze charge ladders by CE are described. Applications of charge ladders and CE to the simultaneous measurement of net charge and hydrodynamic radius of proteins are presented. Techniques for using charge ladders and CE to measure the role of interactions between charged groups on protein stability and ligand binding are also given. The power of this approach lies in the ability to isolate protein charge as an independent and measurable variable in the study of protein stability and function.