Abstract
Expression and purification of recombinant proteins in Escherichia coli is a bedrock technique in biochemistry and molecular biology. Expression optimization requires testing different combinations of solubility tags, affinity purification techniques, and site-specific proteases. This optimization is laborious and time-consuming as these features are spread across different vector series and require different cloning strategies with varying efficiencies. Modular cloning kits based on the Golden Gate system exist, but they are not optimized for protein biochemistry and are overly complicated for many applications, such as undergraduate research or simple screening of protein purification features. An ideal solution is for a single gene synthesis or PCR product to be compatible with a large series of pre-assembled Golden Gate vectors containing a broad array of purification features at either the N or C terminus. To our knowledge, no such system exists. To fulfill this unmet need, we Golden Gate domesticated the pET28b vector and developed a suite of 21 vectors with different combinations of purification tags, solubility domains, visualization/labeling tags, and protease sites. We also developed a vector series with nine different N-terminal tags and no C-terminal cloning scar. The system is modular, allowing users to easily customize the vectors with their preferred combinations of features. To allow for easy visual screening of cloned vectors, we optimized constitutive expression of the fluorescent protein mScarlet3 in the reverse strand, resulting in a red to white color change upon successful cloning. Testing with the model protein sfGFP shows the ease of visual screening, high efficiency of cloning, and robust protein expression. These vectors provide versatile, high-throughput solutions for protein engineering and functional studies in E. coli.