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Systematic Engineering of a Protein Nanocage for High-Yield, Site-Specific Modification

preprint
submitted on 29.09.2018 and posted on 01.10.2018 by Daniel D. Brauer, Emily C. Hartman, Daniel L.V. Bader, Zoe N. Merz, Danielle Tullman-Ercek, Matthew B. Francis

Site-specific protein modification is a widely-used strategy to attach drugs, imaging agents, or other useful small molecules to protein carriers. N-terminal modification is particularly useful as a high-yielding, site-selective modification strategy that can be compatible with a wide array of proteins. However, this modification strategy is incompatible with proteins with buried or sterically-hindered N termini, such as virus-like particles like the well-studied MS2 bacteriophage coat protein. To assess VLPs with improved compatibility with these techniques, we generated a targeted library based on the MS2-derived protein cage with N-terminal proline residues followed by three variable positions. We subjected the library to assembly, heat, and chemical selections, and we identified variants that were modified in high yield with no reduction in thermostability. Positive charge adjacent to the native N terminus is surprisingly beneficial for successful extension, and over 50% of the highest performing variants contained positive charge at this position. Taken together, these studies described nonintuitive design rules governing N-terminal extensions and identified successful extensions with high modification potential.

History

Email Address of Submitting Author

daniel_brauer@berkeley.edu

Institution

UC Berkeley

Country

USA

ORCID For Submitting Author

0000-0001-6974-3476

Declaration of Conflict of Interest

no conflict of interest

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