On-column capping of poly dT media-tethered mRNA accomplishes high capping efficiency, enhanced mRNA recovery, and improved stability against RNase.

ABSTRACT

The messenger RNA (mRNA) 5'-cap structure is indispensable for mRNA translation initiation and stability. Despite its importance, large-scale production of capped mRNA through in vitro transcription (IVT) synthesis using vaccinia capping enzyme (VCE) is challenging, due to the requirement of tedious and multiple pre-and-post separation steps causing mRNA loss and degradation. Here in the present study, we found that the VCE together with 2'-O-methyltransferase can efficiently catalyze the capping of poly dT media-tethered mRNA to produce mRNA with cap-1 structure under an optimized condition. We have therefore designed an integrated purification and solid-based capping protocol, which involved capturing the mRNA from the IVT system by using poly dT media through its affinity binding for 3'-end poly-A in mRNA, in situ capping of mRNA 5'-end by supplying the enzymes, and subsequent eluting of the capped mRNA from the poly dT media. Using mRNA encoding the enhanced green fluorescent protein as a model system, we have demonstrated that the new strategy greatly simplified the mRNA manufacturing process and improved its overall recovery without sacrificing the capping efficiency, as compared with the conventional process, which involved at least mRNA preseparation from IVT, solution-based capping, and post-separation and recovering steps. Specifically, the new process accomplished a 1.76-fold (84.21% over 47.79%) increase in mRNA overall recovery, a twofold decrease in operation time (70 vs. 140 min), and similar high capping efficiency (both close to 100%). Furthermore, the solid-based capping process greatly improved mRNA stability, such that the integrity of the mRNA could be well kept during the capping process even in the presence of exogenously added RNase; in contrast, mRNA in the solution-based capping process degraded almost completely. Meanwhile, we showed that such a strategy can be operated both in a batch mode and in an on-column continuous mode. The results presented in this work demonstrated that the new on-column capping process developed here can accomplish high capping efficiency, enhanced mRNA recovery, and improved stability against RNase; therefore, can act as a simple, efficient, and cost-effective platform technology suitable for large-scale production of capped mRNA.