The gatekeeper position in protein kinases, which is located in the hinge connected the N-beta and C-alpha lobes, is one of the key determinants of chemical selectivity. In many wild type kinases, hydrophobic residues with long side chains, including methionine and leucine, occupy this position. In tyrosine kinases, a threonine is often found, conferring sensitivity to inhibitors such as PP1 and PP2.

The Toxoplasma gondii calcium-dependent protein kinase 1 (TgCDPK1) uniquely features a glycine in this gatekeeper position. We confirmed that this enzyme could be potently inhibited by a series of PP1 derivatives designed to exploit a glycine gatekeeper engineered into kinases from other organisms for the purpose of chemical biology experiments.^[1] In this structure, the bromo-benzyl group in the compound 3BrB-PP1 can be seen occupying the hydrophobic pocket in the gatekeeper position.

References

1. Bishop, A. C. et al., A chemical switch for inhibitor-sensitive alleles of any protein kinase. Nature 407 (6802), 395 (2000).