Today a lot of research is directed towards the development of methods to make protein structure determination faster and more generalised. Automated, general methods for protein expression and purification, robotics for crystallisation and automatic methods for data collection will take structural biology into a new era, that of structural genomics. In two previously performed studies applications were developed for potential use in a structural genomics context. In the first, a fast method to screen for soluble proteins expressed in E. coli using seven N-terminal fusion proteins as solubility enhancing tags was developed. The method was tested on 32 small human proteins suitable for structural study with NMR (Hammarström et al, 2002). In the second, a biophysical screen for fast identification of proteins suitable for structure determination was developed (Woestenenk et al, 2003).
This thesis is an extension of the two previous studies. We have tested the solubility enhancing effect of four N-terminal fusion proteins on 47 cancer and developmental disease related human target proteins, of sizes ranging from 6.6 to 126.5 kDa. We have indications that the solubility enhancing effect is dependent on target protein size. Small proteins of size less than 20 kDa are more likely to be generally affected by the solubility enhancing effect of the fusion partners.
All targets that were overexpressed in the present screen and ten previously uncharacterized targets, related to cancer, from an earlier project were selected for biophysical characterization trials. We were able to purify 15 targets for NMR, CD spectroscopy or both methods. A majority of the targets were estimated to be unstructured or partially unstructured. Only one target was considered directly suitable for structure determination using NMR. The solubility screen and biophysical results were compared to DisEMBL™ and GlobPlot™ disorder predictions of all targets. We found a close match between biophysical data and prediction results. We concluded that, even though we obtain an increased solubility using fusion proteins, many of our targets are likely to be unstructured or partially unstructured and are thus not suitable for structure determination.
Stockholm: KTH , 2005. , v, 66 p.