Study of Protein Hydrodynamics with Light Scatter-in

Proteins are not only important nutrient source for human society, but also play a crucial role in devising various protein-based therapies for many terminal diseases [1]. Therapeutic proteins are usually administrated by the parenteral route. Their dosage form needs to be formulated either as a solution, a suspension or a reconstituted solid dosage form. Therefore, for protein therapeutic products development, protein hydrodynamic behavior in solutions or suspensions is proven to be much more relevant than its isolated and denatured characteristics revealed via advanced microscopy tech-niques. This can be manifested as either protein size monitoring for QC purposes of its purification processes or their charge property control for optimized formulation stability. The critical requirements for these applications often include, but not limited to, non-invasive (in-situ) nature of measurement techniques, easy-of-use and rapidness of tests.

Laser light scattering techniques satisfy these require-ments and provide vital access to the hydrodynamic characteris-tics of biological macromolecules in their native application envi-ronments [2]. Their diffusive displacement (Brownian motion) can be quantified as diffusion coefficient with a dynamic light scattering measurement. In turn, their hydrodynamic radius can be calculated. When placed under an electric filed, the charged proteins undergo a uniform translational movement, the so-called electrophoretic motion or electrophoresis. It results in a Doppler phase/frequency shift of the light signal scattered from the moving proteins, which can be quantitatively evaluated with a carefully designed electrophoretic light scattering experiment. From the measured phase/frequency shift, the charge status of proteins can be extracted.