CK1 Peptide Substrate [pS7] [KRRRAL-pS-VASLPGL]

Product Name: CK1 Peptide Substrate [pS7] [KRRRAL-pS-VASLPGL]

Sequence One Letter Code: KRRRAL-pS-VASLPGL

Sequence Three Letter Code: H-Lys-Arg-Arg-Arg-Ala-Leu-pSer-Val-Ala-Ser-Leu-Pro-Gly-Leu-OH

Molecular Weight: 1603.9

Purity: 95%

Form: Lyophilized

Storage Conditions: - 20 °C

Research Area: peptide substrate

Source / Species: rabbit

Conjugation: Unconjugated

Code Nacres: NA.26

Application: This CK1 peptide substrate is derived from rabbit muscle glycogen synthase and contains a pre-phosphorylated serine at position 7, which primes subsequent phosphorylation at serine 10 by casein kinase I (CK1). CK1 participates in diverse signaling pathways, including circadian rhythm regulation, Wnt signaling, and cell cycle control. The peptide is widely used in kinase assays to evaluate CK1 activity, substrate specificity, and regulatory mechanisms. It supports enzymatic characterization, inhibitor screening, and mechanistic studies of CK1-mediated phosphorylation events in signal transduction research.

Current Research: Casein kinase I (CK1) is a serine/threonine kinase family involved in a broad spectrum of cellular signaling pathways, including circadian rhythm regulation, Wnt/β-catenin signaling, DNA repair, and cell cycle progression. A defining biochemical feature of CK1 is its preference for substrates that are “primed” by prior phosphorylation at a site located several residues N-terminal to the target serine or threonine. The CK1 peptide substrate derived from rabbit muscle glycogen synthase exemplifies this priming requirement: it contains a pre-phosphorylated serine at position 7, which enables efficient phosphorylation of serine 10 by CK1. This design makes it a canonical substrate for in vitro kinase assays and mechanistic studies. The primed substrate motif reflects CK1’s substrate recognition mechanism. CK1 preferentially phosphorylates serine or threonine residues positioned three to four amino acids downstream of an existing phosphoserine or phosphothreonine. In the glycogen synthase–derived peptide, phosphorylation at Ser7 creates a negatively charged determinant that enhances binding affinity and catalytic efficiency toward Ser10. This sequential phosphorylation mechanism is central to CK1’s role in hierarchical phosphorylation cascades, where initial modification by one kinase creates a docking or activation site for CK1. In biochemical assays, this peptide is widely used to quantify CK1 catalytic activity. Recombinant CK1 isoforms—such as CK1δ, CK1ε, or CK1α—are incubated with the primed peptide in the presence of ATP, and phosphorylation at Ser10 is measured using radiometric incorporation, phospho-specific antibodies, fluorescence-based assays, or mass spectrometry. Because the substrate is short, well-defined, and structurally simple, it enables accurate determination of kinetic parameters, including Km and kcat. These measurements provide insight into isoform-specific catalytic efficiency and regulatory modulation. The primed nature of the peptide also makes it a powerful tool for studying CK1 substrate specificity. By comparing phosphorylation of primed versus non-primed variants, researchers can quantify the contribution of upstream phosphorylation to catalytic turnover. Mutational substitution of the phosphoserine at position 7 with alanine or aspartate can further clarify the structural requirements for CK1 recognition. Such experiments have been instrumental in defining consensus motifs and understanding how CK1 discriminates among potential substrates in complex signaling networks. CK1 plays a prominent role in circadian rhythm regulation, particularly through phosphorylation of PER (Period) proteins, which controls their stability and nuclear localization. CK1 activity toward primed substrates influences circadian periodicity and has been linked to familial advanced sleep phase disorders. The glycogen synthase–derived peptide provides a convenient surrogate substrate for evaluating CK1 activity under conditions that mimic regulatory modulation observed in circadian systems. In Wnt/β-catenin signaling, CK1 participates in the multi-step phosphorylation of β-catenin and other pathway components. Sequential phosphorylation events often involve priming by upstream kinases, followed by CK1-mediated modification. The primed peptide model reflects this hierarchical phosphorylation logic and supports mechanistic dissection of signal-dependent regulation. By incorporating this substrate into kinase assays, researchers can assess how regulatory proteins, post-translational modifications, or small-molecule inhibitors influence CK1 catalytic behavior. The peptide is also widely applied in inhibitor screening and drug discovery. CK1 dysregulation has been implicated in cancer, neurodegenerative disorders, and inflammatory diseases. Small-molecule inhibitors targeting CK1 isoforms are evaluated using peptide-based assays to determine IC50 values and inhibition kinetics. Because the substrate reflects CK1’s natural preference for primed sequences, assay results are highly relevant to physiological phosphorylation events. Overall, the glycogen synthase–derived CK1 peptide substrate, featuring a pre-phosphorylated serine at position 7, provides a robust and mechanistically informative platform for studying primed phosphorylation. Its application in enzymatic characterization, specificity analysis, and inhibitor evaluation supports a wide range of research efforts focused on CK1-mediated signal transduction and regulatory network control.