Plasmid Topology and Digest Analysis Using a GTxResolve™ 250 Å Slalom Chromatography Column

Importance of the Topic

Plasmid DNA underpins gene and cell therapies, serving as templates for recombinant protein production and mRNA synthesis via in vitro transcription. Ensuring high purity and correct topology in supercoiled, open-circular, and linear forms is essential for therapeutic efficacy and safety. Traditional electrophoretic methods can be time-consuming and require large sample amounts, driving interest in faster, higher-throughput alternatives.

Objectives and Overview

This application note demonstrates slalom chromatography on a GTxResolve™ 250 Å Slalom Column to:

• Separate plasmid topological isomers in under five minutes
• Quantify linearization efficiency following restriction enzyme digestion
• Detect low-abundance open-circular and linear impurities in large plasmid constructs (≥7 kbp)
• Confirm the presence of gene inserts through double-digest analysis

Methodology and Instrumentation

Analyses were conducted on an ACQUITY UPLC I-Class Bio system with a quaternary solvent manager, tunable UV detector, FTN sample manager, and pre-/post-column heaters. The GTxResolve™ 250 Å Slalom Column (4.6×300 mm, 2.5 µm) with MaxPeak high performance surfaces was employed. Mobile phase comprised 1X TAE buffer (40 mM Tris-acetate, 1 mM EDTA, pH 8.3) with 10% acetonitrile. Key parameters included isocratic flow (0.5–1.3 mL/min), column temperatures between 5 °C and 40 °C, and a 40 Hz sampling rate. Plasmid samples (pBR322, pCMV-Cas9, pCMV-Cas9-GFP) were subjected to EcoRI, NheI, and XbaI digestions to generate supercoiled, linear, and open-circular species.

Main Results and Discussion

Slalom chromatography resolved supercoiled and linear forms of pBR322 within ~1.14 to 1.28 minutes, enabling rapid assessment of linearization efficiency. At 5 °C, larger plasmids (7–8 kbp) displayed distinct early and late eluting peaks corresponding to open-circular and linear impurities alongside the main supercoiled species. Double digestion of pCMV-Cas9 with NheI and XbaI released a ~4.1 kbp insert and ~2.9 kbp backbone, which eluted with a 0.077-minute difference. Compared to agarose gel electrophoresis, slalom chromatography achieved a fivefold sensitivity gain, requiring only 40 ng versus 200 ng sample.

Benefits and Practical Applications

• High-resolution separation of plasmid isoforms in under five minutes
• Minimal sample consumption and low nonspecific adsorption
• Integration with standard UPLC platforms for high-throughput workflows
• Quantitative monitoring of restriction digestion and impurity levels
• Rapid confirmation of gene insert integrity in recombinant constructs

Future Trends and Applications

Coupling slalom chromatography with anion exchange techniques could improve resolution of smaller plasmids (<7 kbp). Fine-tuning flow rate, solvent viscosity, and shear forces offers further selectivity optimization. Advances in column packing and surface chemistries may broaden applications for rapid quality control in cell and gene therapy manufacturing.

Conclusion

Slalom chromatography using the GTxResolve™ 250 Å Slalom Column provides a robust, high-throughput alternative to electrophoretic methods for plasmid topology analysis. Its ability to resolve supercoiled, open-circular, and linear species in under five minutes with enhanced sensitivity supports streamlined workflows in research and biomanufacturing.

Reference

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