Accuracy of Protein Size Estimates Based on Light Scattering Measurements

There are two types of light scattering measurements: static light scattering (SLS) and dynamic light scattering (DLS). The SLS method is used to estimate the molecular weight (MW) of particles by measuring the time-averaged intensity of light scattered by the particles, whereas the DLS method is used to estimate the diffusion coefficient of particles by observing the time-correlation of scattered light intensity. These techniques have recently been applied to the investigation of the aggregation, denaturation and folding, and complex formation of proteins in solution. However, the accuracy of protein size measurement by light scattering is poorly understood. In the present study, we carried out the size measurements of five globular proteins by SLS and DLS at a detection angle of 90 ̊ and compared these data to measurements made by size exclusion chromatography (SEC). The difference (%) between the MW estimated from each method and the MW calculated from the amino acid sequence (namely the calibration residual error) was regarded as an index of measurement accuracy. The averaged calibration residual errors were 5.2 and 4.7 for SEC and SLS measurements, respectively. For the DLS measurements, the extrapolation of the apparent hydrodynamic radii to a protein concentration of zero may effectively eliminate the interparticle and hydrodynamic interactions and significantly reduced the averaged calibration residual error to 4.8%. Our results suggested that the size of globular proteins can be estimated using light scattering measurements with an accuracy equivalent to that of SEC.