SOLUTION X-RAY SCATTERING STUDIES ON PROTEIN INTERACTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Systematic studies of the structure factor of a protein in solution by small angle scattering can extract electrostatic properties of the protein and protein-protein interaction. We conducted initial studies on the interactions of lysozyme, which has been extensively studied in the past in a number of published protein interaction studies. It is necessary to carry out small angle X-ray scattering measurements over a wide range of protein and salt concentrations in this class of studies. Dilute protein samples are used to obtain the form factor and highly concentrated solutions are needed for determining the structure factor. In the absence of salt the electrostatic interactions among protein molecules dominates while the attractive short-range potentials become detectable at high salt concentrations. Our preliminary results demonstrate that we can determine the lysozyme form factor at concentrations as low as 0.5 mg/ml at BL 4-2. We were able to overcome radiation damage problems we had previously observed with lysozyme, using the flow cell in combination with the solution dispenser. We plan on studying the effects of glycerol, an agent known to help minimize radiation damage on the protein interaction potential. Also studied will be the effects of L-Arg and L-Glu, which together have been reported to improve protein solubility.