Co-expression of the RPS6KB1 and PDPK1 genes for production of activated p70S6K1 using bac-to-bac baculovirus expression system

Ribosomal protein S6 kinase 1 (p70S6K1) is a member of the AGC family of serine/threonine kinases which plays a role in various cellular processes, including protein synthesis, cell growth, and survival. Dysregulation of p70S6K1, characterized by its overexpression and/or hyperactivation, has been implicated in numerous human pathologies, particularly in several types of cancer. Therefore, generating active, recombinant p70S6K1 is critical for investigating its role in cancer biology and for developing novel diagnostic or therapeutic approaches.

Here, we report a reliable and efficient methodology for the expression and purification of highly active p70S6K1 (His-actS6K1) in quantity and quality that is suitable for biochemical/biophysical studies and high-throughput enzymatic assays. Our developed methodology offers a rapid and cost-effective approach for producing constitutively active His-actS6K1, which can be utilized in academic research and biotechnology.

The baculovirus dual expression system was utilized, enabling the co-expression of two recombinant proteins in infected cells: (a) His-tagged S6K1 with a deletion of the C-terminal autoinhibitory motif and a phosphomimetic mutation at the mTORC1 phosphorylation site (T389D), and (b) untagged PDPK1 lacking the PH domain. The high activity of the purified kinase was confirmed by immunoblotting, as well as by Kinase-Glo and AlphaScreen kinase assays.

Efficient expression of both recombinant proteins was achieved, resulting in highly pure preparations of His-tagged p70S6K1. The high activity of the purified kinase was confirmed through multiple kinase assays, demonstrating significantly higher levels of substrate phosphorylation compared to the tested commercial product.