The hallmark of AGC kinase functional divergence is its C-terminal tail, a cis-acting regulatory module

Abstract

The catalytic activities of eukaryotic protein kinases (EPKs) are regulated by movement of the C-helix, movement of the N and C lobes upon ATP binding, and movement of the activation loop upon phosphorylation. Statistical analysis of the selective constraints associated with AGC kinase functional divergence reveals conserved interactions between these regulatory regions and three regions of the C-terminal tail (C-tail): the N-lobe tether (NLT), the active-site tether (AST), and the C-lobe tether (CLT). The NLT serves as a docking site for an upstream kinase PDK1 and, upon activation, positions the C-helix within the ATP binding pocket. The AST directly interacts with the ATP binding pocket, and the CLT interacts with the interlobe linker and the αC–β4 loop, which appears to serve as a hinge for C-helix movement. The C-tail is a hallmark of AGC functional divergence inasmuch as most of the conserved core residues that distinguish AGC kinases from other EPKs are associated with the NLT, AST, or CLT. Moreover, several AGC catalytic core conserved residues that interact with the C-tail strikingly diverge from the canonical residues observed at corresponding positions in nearly all other EPKs, suggesting that the catalytic core may have coevolved with the C-tail in AGC kinases. These observations, along with the fact that the C-tail is needed for catalytic activity suggests that the C-tail is a cis-acting regulatory module that can also serve as a regulatory “handle,” to which trans-acting cellular components can bind to modulate activity.

Localization and quaternary structure of the PKA RIβ holoenzyme

“…The active site tether (AST) that links these two segments is dynamic and locks the kinase into a closed conformation in the presence of nucleotides (Fig. S3) (23,25,26). The FDDY motif (residues 327-330) is the signature motif of the AST and interacts directly with ATP.…”

Congenital disease SNPs target lineage specific structural elements in protein kinases

“…This loop is the only part of the N-lobe that is firmly anchored to the C-lobe and serves as a hinge point for C-helix movement (26). More recent studies have suggested a role for this motif in kinase regulation (27), because variations within this loop appear to favor alternative modes of C-helix positioning (21,28). Mutations at this site produce severe (29,30) and/or dominant-negative effects (31).…”

“…In Cdk2, for instance, the K92 equivalent (I52) directly interacts with cyclin A, which is a key regulator of Cdk2 activity (20). Likewise, in AGC kinases, K92 positions the C-terminal tail, which serves as a cis-regulatory element (21). Moreover, K92 is strategically located relative to the kinase conserved E91, which positions the ATP by forming a salt bridge interaction with K72.…”

Cotranslational cis -phosphorylation of the COOH-terminal tail is a key priming step in the maturation of cAMP-dependent protein kinase

“…The C-tail is anchored to both the N-and C-lobes, and it is an essential, conserved feature of all AGC kinases, (Fig. 1A) (3). The turn motif and HM sites wrap around the N-lobe and position it for catalysis (3,4).…”

“…A small N-terminal lobe (N-lobe) and a larger carboxyl-terminal helical lobe (C-lobe) create a cleft between the two lobes where the ATP substrate binds. All EPKs have an activation loop in the C-lobe that typically harbors a conserved activation loop phosphorylation site, which is a major regulatory site (2)(3)(4). Other kinase-specific phosphorylation sites may be auto-or trans-phosphorylated by heterologous kinases.…”