Zeta potential measurements for evaluation the quality of protein samples for crystallization.

Scientific Instrumentation Business Div., Sysmex Corporation* Mol Logics, Japan** Institute for Protein Research, Osaka University, Japan***
â—‹Kohei Shiba* Koji Inaka** Shigeru Sugiyama** Kyoko Ogasahara*** Atsushi Nakagawa***

Recent progress in structure determination of proteins allows us to reveal the interactions of protein molecules at atomic level. NMR and X-ray crystallography are widely used for determination of the three-dimensional structure of the proteins in detail. In both techniques, preparation of good samples is now the most difficult and important step. In addition, crystallization of the sample is required for X-ray crystallography. However, it is often met the serious problem that the crystals cannot easily be obtained, after enormous number of trials of crystallization has been attempted. Gel-electrophoresis, such as SDS-PAGE and Native-Page, gel-filtration and dynamic light scattering measurement are often used for evaluation of quality of samples and these measurements sometimes used for evaluation of possibility of crystallization. However, these measurements are not the magic bullet for evaluation of possibilities of crystallization.
Zeta potential is often used for judging the dispersion stability of colloidal or some other nano-particles. Roughly speaking, the zeta potential shows surface potential effecting around the particles. Zeta potentials at stable dispersion condition of the particles often show the values higher than +-25mV.
We will report here the results of Zeta potential measurement of proteins for estimation of the quality of the samples and relationship between Zeta potential and quality of crystals.