An autoinhibitory tyrosine motif in the cell-cycle-regulated Nek7 kinase is released through binding of Nek9.
Bottom Line: Tyrosine mutants of Nek7 and the related kinase Nek6 are constitutively active.The activity of Nek6 and Nek7, but not the tyrosine mutant, is increased by interaction with the Nek9 noncatalytic C-terminal domain, suggesting a mechanism in which the tyrosine is released from its autoinhibitory position.The autoinhibitory conformation is common to three Neks and provides a potential target for selective kinase inhibitors.
Affiliation: Institute of Cancer Research, London, UK.
Mitosis is controlled by multiple protein kinases, many of which are abnormally expressed in human cancers. Nek2, Nek6, Nek7, and Nek9 are NIMA-related kinases essential for proper mitotic progression. We determined the atomic structure of Nek7 and discovered an autoinhibited conformation that suggests a regulatory mechanism not previously described in kinases. Additionally, Nek2 adopts the same conformation when bound to a drug-like molecule. In both structures, a tyrosine side chain points into the active site, interacts with the activation loop, and blocks the alphaC helix. Tyrosine mutants of Nek7 and the related kinase Nek6 are constitutively active. The activity of Nek6 and Nek7, but not the tyrosine mutant, is increased by interaction with the Nek9 noncatalytic C-terminal domain, suggesting a mechanism in which the tyrosine is released from its autoinhibitory position. The autoinhibitory conformation is common to three Neks and provides a potential target for selective kinase inhibitors.
Related in: MedlinePlus
Mentions: Nek6 and Nek7 are 86% identical within their catalytic domains but are highly divergent in their N-terminal extensions (Figure 6A). The N-terminal extension to the catalytic domain of Nek7 (NTE, residues 20–33) adopts a highly unusual structure, an extended ordered loop wrapped around the side chain of Asn33 (Figure 6B). This side chain forms three H-bonds with the NTE backbone: the backbone oxygen of Gly27 and the backbone oxygen of Arg23 form H-bonds with the Asn33 side-chain nitrogen, and the backbone nitrogen of Arg23 forms an H-bond with the Asn33 side-chain oxygen. Substitution of Asn33 for any other amino acid would disrupt this network of H-bonds and destabilize the local structure. Notably, the equivalent position in Nek6 is an aspartic acid (Figures 6A and 6B). Mapping the sequence conservation between Nek6 and Nek7 onto the structure of Nek7 shows that the two kinases share an almost completely identical front face (Figure 6C, left), with most of the differences lying on the back face (Figure 6C, right). The large patch of nonconserved residues on the N lobe includes the ordered NTE of Nek7 and residues on the core catalytic domain that contact the NTE. The NTE of Nek7 sits on the core catalytic domain on a largely hydrophobic surface between β4 and the β2-β3 loop (Figure 6B). The differences between Nek6 and Nek7 in this region are hydrophilic for hydrophobic substitutions, suggesting that this region of Nek6 may be solvent exposed. For example the sequence “GVP” on β3 of Nek7 is replaced by “RKT” in Nek6, and Ala99Nek7 is replaced by aspartic acid. These changes, and the presence of aspartic acid at the equivalent position to Asn33Nek7, suggest that Nek6 does not have an NTE-like motif similar to that found in Nek7.