New analytical techniques for the quantification of protein charge and hydrodynamic size

Net charge and hydrodynamic size of proteins affect the production, processing, and purification of proteins in vitro as well as their rates of transport in vivo. Because charge and size play a role in such a variety of applications, it is important to not only be able to quantify them but also to be able to measure their impacts in processes such as diffusion, partitioning, and binding. To this end, analytical techniques are needed to allow for (1) the measurement of protein charge, (2) the isolation of protein charge as an independent variable, (3) the quantification of hydrodynamic size of a protein, and (4) the isolation of hydrodynamic size of a protein as an independent variable. This thesis demonstrates the development of analytical techniques to accomplish these objectives which, in turn, provide for a direct measure of the absolute and relative roles of protein charge and hydrodynamic size in various applications in biology and biotechnology.; Charge ladders, a series of protein derivatives synthesized by the random, partial chemical modification of charged groups on a protein, have been used previously for both the isolation and quantification of protein charge. When separated using capillary electrophoresis (CE), these derivatives have allowed for determination of the net charge and hydrodynamic size of the unmodified protein. Doing so has required the assumption that the change in protein charge upon modification of one of its charged groups, DeltaZ, is equal to the initial charge of that group. In this thesis, it is shown that this assumption is not always accurate due to the effects of cooperativity in proton binding between charged groups on the protein. The error in the values of charge and hydrodynamic size obtained from charge ladder measurements is always less than or equal to the error in DeltaZ. This result impacts the ability of charge ladders to be used as a tool to measure quantitative effects of charge on protein properties.; A technique is also presented for the determination of the size of proteins from measurement of their diffusivities. This technique, based on Taylor dispersion, allows for the rapid, efficient measurement of solute diffusivities particularly when performed using a commercial CE instrument. (Abstract shortened by UMI.)...