Nature Methods
- 3, 845 - 854 (2006)
Published online: 21 September 2006; | doi:10.1038/nmeth932
In vivo and in vitro protein solubility assays using split GFPStéphanie Cabantous & Geoffrey S Waldo
Bioscience Division, MS-M888, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545, USA.
Correspondence should be addressed to Geoffrey S Waldo waldo@lanl.gov The rapid assessment of protein solubility is essential for evaluating expressed proteins and protein variants for use as reagents for downstream studies. Solubility screens based on antibody blots are complex and have limited screening capacity1,
2,
3. Protein solubility screens using split  -galactosidase in vivo
4 and in vitro
5 can perturb protein folding. Split GFP used for monitoring protein interactions folds poorly6, and to overcome this limitation, we recently developed a protein-tagging system based on self-complementing split GFP7 derived from an exceptionally well folded variant of GFP termed 'superfolder GFP'8. Here we present the step-by-step procedure of the solubility assay using split GFP. A 15-amino-acid GFP fragment, GFP 11, is fused to a test protein. The GFP 1–10 detector fragment is expressed separately. These fragments associate spontaneously to form fluorescent GFP. The fragments are soluble, and the GFP 11 tag has minimal effect on protein solubility and folding7. We describe high-throughput protein solubility screens amenable both for in vivo and in vitro formats. The split-GFP system is composed of two vectors used in the same strain: pTET GFP 11 and pET GFP 1–10 (Fig. 1 and Supplementary Note online). The gene encoding the protein of interest is cloned into the pTET GFP 11 vector (resulting in an N-terminal fusion) and transformed into Escherichia coli BL21 (DE3) cells containing the pET GFP 1–10 plasmid. We also describe how this system can be used for selecting soluble proteins from a library of variants (Box 1). The large screening power of the in vivo assay combined with the high accuracy of the in vitro assay point to the efficiency of this two-step split-GFP tool for identifying soluble clones suitable for purification and downstream applications.
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T4 DNA ligase buffer (Invitrogen)
