The DNA Damage Repair Function of Fission Yeast CK1 Involves Targeting Arp8, a Subunit of the INO80 Chromatin Remodeling Complex.

The CK1 family are conserved serine/threonine kinases with numerous substrates and cellular functions. The fission yeast CK1 orthologues Hhp1 and Hhp2 were first characterized as regulators of DNA repair, but the mechanism(s) by which CK1 activity promotes DNA repair had not been investigated. Here, we found that deleting Hhp1 and Hhp2 or inhibiting CK1 catalytic activities in yeast or in human cells increased double-strand breaks (DSBs).

Substrate displacement of CK1 C-termini regulates kinase specificity.

CK1 kinases participate in many signaling pathways, and their regulation is of meaningful biological consequence. CK1s autophosphorylate their C-terminal noncatalytic tails, and eliminating these tails increases substrate phosphorylation in vitro, suggesting that the autophosphorylated C-termini act as inhibitory pseudosubstrates. To test this prediction, we comprehensively identified the autophosphorylation sites on Hhp1 and human CK1ε.

Substrate displacement of CK1 C-termini regulates kinase specificity.

CK1 kinases participate in many signaling pathways; how these enzymes are regulated is therefore of significant biological consequence. CK1s autophosphorylate their C-terminal non-catalytic tails, and eliminating these modifications increases substrate phosphorylation in vitro, suggesting that the autophosphorylated C-termini act as inhibitory pseudosubstrates. To test this prediction, we comprehensively identified the autophosphorylation sites on Hhp1 and human CK1ε.

Kinase domain autophosphorylation rewires the activity and substrate specificity of CK1 enzymes.

CK1s are acidophilic serine/threonine kinases with multiple critical cellular functions; their misregulation contributes to cancer, neurodegenerative diseases, and sleep phase disorders. Here, we describe an evolutionarily conserved mechanism of CK1 activity: autophosphorylation of a threonine (T220 in human CK1δ) located at the N terminus of helix αG, proximal to the substrate binding cleft. Crystal structures and molecular dynamics simulations uncovered inherent plasticity in αG that increased upon T220 autophosphorylation.

Phosphorylation in the intrinsically disordered region of F-BAR protein Imp2 regulates its contractile ring recruitment.

The F-BAR protein Imp2 is an important contributor to cytokinesis in the fission yeast Schizosaccharomyces pombe. Because cell cycle-regulated phosphorylation of the central intrinsically disordered region (IDR) of the Imp2 paralog Cdc15 controls Cdc15 oligomerization state, localization and ability to bind protein partners, we investigated whether Imp2 is similarly phosphoregulated. We found that Imp2 is endogenously phosphorylated on 28 sites within its IDR, with the bulk of phosphorylation being constitutive.

Spatiotemporal regulation of the Dma1-mediated mitotic checkpoint coordinates mitosis with cytokinesis.

During cell division, the timing of mitosis and cytokinesis must be ordered to ensure that each daughter cell receives a complete, undamaged copy of the genome. In fission yeast, the septation initiation network (SIN) is responsible for this coordination, and a mitotic checkpoint dependent on the E3 ubiquitin ligase Dma1 and the protein kinase CK1 controls SIN signaling to delay cytokinesis when there are errors in mitosis. The participation of kinases and ubiquitin ligases in cell cycle checkpoints that maintain genome integrity is conserved from yeast to human, making fission yeast an excellent model system in which to study checkpoint mechanisms.

Relief of the Dma1-mediated checkpoint requires Dma1 autoubiquitination and dynamic localization.

Chromosome segregation and cell division are coupled to prevent aneuploidy and cell death. In the fission yeast Schizosaccharomyces pombe, the septation initiation network (SIN) promotes cytokinesis, but upon mitotic checkpoint activation, the SIN is actively inhibited to prevent cytokinesis from occurring before chromosomes have safely segregated. SIN inhibition during the mitotic checkpoint is mediated by the E3 ubiquitin ligase Dma1.

A bifurcated signaling cascade of NIMA-related kinases controls distinct kinesins in anaphase.

In mitosis, cells undergo a precisely orchestrated series of spatiotemporal changes in cytoskeletal structure to divide their genetic material. These changes are coordinated by a sophisticated network of protein-protein interactions and posttranslational modifications. In this study, we report a bifurcation in a signaling cascade of the NIMA-related kinases (Neks) Nek6, Nek7, and Nek9 that is required for the localization and function of two kinesins essential for cytokinesis, Mklp2 and Kif14.

Crystal structure of acivicin-inhibited gamma-glutamyltranspeptidase reveals critical roles for its C-terminus in autoprocessing and catalysis.

Helicobacter pylori gamma-glutamyltranspeptidase (HpGT) is a general gamma-glutamyl hydrolase and a demonstrated virulence factor. The enzyme confers a growth advantage to the bacterium, providing essential amino acid precursors by initiating the degradation of extracellular glutathione and glutamine. HpGT is a member of the N-terminal nucleophile (Ntn) hydrolase superfamily and undergoes autoprocessing to generate the active form of the enzyme.