High-Throughput Purification of Protein Kinases from Escherichia coli and Insect Cells

Enabling pseudokinases as potential drug targets

Pseudokinases play significant roles in disease development. Similar to active kinases, their cellular functions can be targeted pharmacologically. But notably, instead of inhibiting an enzymatic activity, drug-like molecules act by stabilizing distinct pseudokinase conformations, by interfering with protein interactions, or by inducing proteasomal degradation. Herein, we describe our approach of enabling particular pseudokinases as potential drug targets. The method starts with obtaining recombinant proteins for assay development and for biochemical evaluation. The next step is to probe the pseudoactive site as a binding pocket for small molecules, providing initial insight into binding modes and even candidate chemotypes. Finally, structural features of pseudokinase:inhibitor complexes are explored. Taken together, we provide detailed method descriptions for essential inhibitor development technologies.

Comparative expression of soluble, active human kinases in specialized bacterial strains

Kinases act as molecular switches for cellular functions and are involved in multiple human pathogeneses, most notably cancer. There is a continuous need for soluble and active kinases for in-vitro drug discovery and structural biology purposes. Kinases remain challenging to express using Escherichia coli, the most widely utilized host for heterologous expression. In this work, four bacterial strains, BL21 (DE3), BL21 (DE3) pLysS, Rosetta, and Arctic Express, were chosen for parallel expression trials along with BL21 (DE3) complemented with folding chaperones DnaJ/K and GroEL/ES to compare their performance in producing soluble and active human kinases. Three representative diverse kinases were studied, Epidermal Growth Factor Receptor kinase domain, Aurora Kinase A kinase domain, and Mitogen-activated protein Kinase Kinase. The genes encoding the kinases were subcloned into pET15b bacterial plasmid and transformed into the bacterial strains. Soluble kinase expression was tested using different IPTG concentrations (1–0.05 mM) at varying temperatures (37°C– 10°C) and induction times (3–24 hours). The optimum conditions for each kinase in all strains were then used for 1L large scale cultures from which each kinase was purified to compare yield, purity, oligomerization status, and activity. Although using specialized strains achieved improvements in yield and/or activity for the three kinases, none of the tested strains was universally superior, highlighting the individuality in kinase expression.

Plasmodium Kinases as Potential Drug Targets for Malaria: Challenges and Opportunities

Protein and phosphoinositide kinases have been successfully exploited as drug targets in various disease areas, principally in oncology. In malaria, several protein kinases are under investigation as potential drug targets, and an inhibitor of Plasmodium phosphatidylinositol 4-kinase type III beta (PI4KIIIβ) is currently in phase 2 clinical studies. In this Perspective, we review the potential of kinases as drug targets for the treatment of malaria. Kinases are known to be readily druggable, and many are essential for parasite survival. A key challenge in the design of Plasmodium kinase inhibitors is obtaining selectivity over the corresponding human orthologue(s) and other human kinases due to the highly conserved nature of the shared ATP binding site. Notwithstanding this, there are some notable differences between the Plasmodium and human kinome that may be exploitable. There is also the potential for designed polypharmacology, where several Plasmodium kinases are inhibited by the same drug. Prior to starting the drug discovery process, it is important to carefully assess potential kinase targets to ensure that the inhibition of the desired kinase will kill the parasites in the required life-cycle stages with a sufficiently fast rate of kill. Here, we highlight key target attributes and experimental approaches to consider and summarize the progress that has been made targeting Plasmodium PI4KIIIβ, cGMP-dependent protein kinase, and cyclin-dependent-like kinase 3.