Noteworthy progress on this project has been made recently in two areas: understanding the mechanism by which certain highly soluble proteins enhance the solubility and promote the folding of their fusion partners, and the development of baculovirus vectors for the secretion of N-terminally His-tagged proteins from insect cells. Building on our previous investigation of the mechanism by which Escherichia coli maltose binding protein (MBP) enhances the solubility of its fusion partners, we have now shown that E. coli NusA, a completely unrelated protein that is also a very effective solubility enhancer, operates by the same or a very similar mechanism, suggesting that diverse solubility-enhancing proteins work in a fundamentally similar manner. We have also shown that MBP must be joined to the N-terminus of its fusion partner (rather than to its C-terminus) in order to enhance its solubility. This suggests that MBP needs to emerge first from the active ribosome for it to be fully functional as a solubility enhancer and is consistent with a model in which folded MBP binds to partially folded passenger proteins to inhibit their intermolecular aggregation. Additionally, baculovirus expression vectors were designed to secrete recombinant proteins using either the honeybee melittin or gp67 signal peptides in such a manner that the secreted proteins retain an N-terminal polyhistidine tag that can be removed by digestion with TEV protease. Both signal peptides were equally effective at promoting the secretion of MBP and green fluorescent protein (GFP). Moreover, both secreted proteins were processed correctly and could be captured on a Ni-NTA column. The yield of secreted GFP was high enough that the protein could be observed on a Coomassie-stained gel without Western blotting. The yield of secreted MBP was exceptionally high, constituting far and away the most abundant protein in the conditioned medium. Hence, these vectors are a useful addition to the toolbox for protein expression in insect cells.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Investigator-Initiated Intramural Research Projects (ZIA)
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Raran-Kurussi, Sreejith; Waugh, David S (2017) Expression and Purification of Recombinant Proteins in Escherichia coli with a His6 or Dual His6-MBP Tag. Methods Mol Biol 1607:1-15
Raran-Kurussi, Sreejith; Cherry, Scott; Zhang, Di et al. (2017) Removal of Affinity Tags with TEV Protease. Methods Mol Biol 1586:221-230
Raran-Kurussi, Sreejith; Waugh, David S (2016) A dual protease approach for expression and affinity purification of recombinant proteins. Anal Biochem 504:30-7
Waugh, David S (2016) Crystal structures of MBP fusion proteins. Protein Sci 25:559-71
Waugh, David S (2016) The remarkable solubility-enhancing power of Escherichia coli maltose-binding protein. Postepy Biochem 62:377-382
Raran-Kurussi, Sreejith; Keefe, Karina; Waugh, David S (2015) Positional effects of fusion partners on the yield and solubility of MBP fusion proteins. Protein Expr Purif 110:159-64
Raran-Kurussi, Sreejith; Waugh, David S (2014) Unrelated solubility-enhancing fusion partners MBP and NusA utilize a similar mode of action. Biotechnol Bioeng 111:2407-11
Needle, Danielle; Waugh, David S (2014) Rescuing aggregation-prone proteins in Escherichia coli with a dual His?-MBP tag. Methods Mol Biol 1177:81-94
Raran-Kurussi, Sreejith; Tözsér, József; Cherry, Scott et al. (2013) Differential temperature dependence of tobacco etch virus and rhinovirus 3C proteases. Anal Biochem 436:142-4
Austin, Brian P; Waugh, David S (2012) Isolation of Metarhizium anisopliae carboxypeptidase A with native disulfide bonds from the cytosol of Escherichia coli BL21(DE3). Protein Expr Purif 82:116-24

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