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| Description | FAM-CSKtide is a dedicated substrate for C-terminal Src kinase (which phosphorylates the C-terminal inhibitory Tyr of Src-family kinases). FAM labeling reports CSK tyrosine-kinase activity through phosphorylation-induced charge/FP changes, used for kinase quantification, inhibitor screening and Src-pathway studies. |
| Structure type | Linear tyrosine-kinase substrate (CSKtide, FAM-labeled) |
| Solubility | Readily soluble in water/PBS |
| Storage | Powder, −20°C, dry, light-protected |
Product Basic Information Table
| Product Standard English Name | Product Abbreviation / Alias | Function Tags (comma-separated) | Core Structure | Molecular Formula | Exact Mass (Da) | Average MW (Da) | Salt Form | Length (aa) |
| FAM-CSKtide (N-terminally 5-FAM-labeled C-terminal Src kinase optimal substrate Lys-Lys-Lys-Lys-Glu-Glu-Ile-Tyr-Phe-Phe-Phe-Gly-NH2) | 5-FAM-KKKKEEIYFFFG-NH2; FAM-Csk peptide; CSKtide-FAM; H-5-FAM-KKKKEEIYFFFG-NH2; Csk optimal fluorescent substrate; C-terminal Src kinase substrate | fluorescent peptide, 5-FAM carboxyfluorescein, Csk (C-terminal Src kinase) tyrosine kinase substrate, Tyr phosphorylation, Csk optimal substrate, homogeneous fluorescence kinase assay, anti-pTyr/TR-FRET assay, Src-family negative regulation, light-sensitive | Linear 12-mer; 5-FAM (net addition C21H10O6) conjugated via an amide bond to the N-terminal alpha-amine; sequence 5-FAM-Lys-Lys-Lys-Lys-Glu-Glu-Ile-Tyr-Phe-Phe-Phe-Gly-NH2 (KKKKEEIYFFFG-NH2); C-terminal amide (-NH2); Tyr8 is the Csk phosphorylation site; four N-terminal Lys enhance solubility and kinase-domain binding; acidic Glu5-6 upstream of Tyr and hydrophobic Phe-Phe-Phe downstream match Csk active-site substrate preference (acidic N-side, hydrophobic C-side); after N-terminal FAM acylation and C-terminal amidation the net charge is ~+2 (four Lys +4, two Glu -2); FAM (Ex~495/Em~517 nm) enables homogeneous quantification of phosphorylated substrate/product by mobility shift or TR-FRET; no Trp/Cys/Met | C99H125N17O23 | 1919.91 | 1921.19 | C-terminal amide (-NH2); N-terminal 5-FAM fluorescent label; free acid; acetate/TFA available on request | 12 |
Physicochemical Solubility & Storage Parameters
| Product Code | Appearance | Long-term Storage | Short-term Storage | Solution Stability | Solid Powder Stability |
| PEP-FAMCSK-01 | Yellow to tan powder (5-FAM coloration); hygroscopic | Store at -20C, sealed, desiccated, strictly protected from light (amber tube/aluminum foil), ~2 years. Aliquot to avoid freeze-thaw. FAM is light-sensitive-keep in the dark to prevent photobleaching and quenching. | 2-8C, protected from light, ~1 month; working aliquots at -20C in the dark; avoid repeated freeze-thaw; ship cold-chain with light protection. | Good water solubility (four N-terminal Lys/basic residues, net charge ~+2); dissolves in water or neutral buffer (PBS, HEPES, pH 7.0-7.4) to mg/mL. For tyrosine kinase reactions use HEPES/Tris buffer (with Mn2+ or Mg2+, ATP), pH 7.4, 30C. Keep solutions light-protected; the Tyr-containing substrate must be kept free of phosphatase contamination (add phosphatase inhibitors/orthovanadate). The FAM-labeled version suits Caliper/mobility-shift chips (Tyr phosphorylation adds negative charge, shifting mobility), TR-FRET/LANCE (Eu-labeled anti-pTyr antibody), homogeneous fluorescence Csk assays, and high-throughput inhibitor screening. | solid stable ~2 years at -20C, sealed, desiccated and light-protected; FAM photobleaching and caking from moisture are the main degradation factors-keep dry and dark, minimize air exposure. |
Functional Description
| Product Code | Frontend Short Summary | Detailed Biological Function Description | Applicable Research Areas (comma-separated) | Targets / Pathways |
| PEP-FAMCSK-01 | N-terminally 5-FAM-labeled optimal synthetic substrate peptide for C-terminal Src kinase (Csk), KKKKEEIYFFFG-NH2, phosphorylated at Tyr8; for homogeneous fluorescence Csk kinase assays, Csk inhibitor screening and studies of Src-family negative regulation. Protect from light. | Csk (C-terminal Src kinase) is a non-receptor tyrosine kinase whose central physiological role is to phosphorylate the C-terminal negative-regulatory tyrosine of Src-family kinases (c-Src, Fyn, Lck, Lyn, Yes)-Tyr527 in c-Src. The resulting pTyr binds the kinase's own SH2 domain intramolecularly, locking the kinase in an autoinhibited (closed) conformation and thereby suppressing Src-family pro-proliferative, focal-adhesion, migratory and immune-receptor signaling. Csk is thus the key negative regulator of Src family kinases and is important in T-cell receptor signaling, cell migration, and tumor suppression/progression. CSKtide (KKKKEEIYFFFG-NH2) is an optimized substrate selected by oriented peptide libraries for high specificity and affinity toward Csk: Tyr8 is the phosphorylation site; the four N-terminal Lys improve solubility and engage the kinase basic pocket; the acidic Glu-Glu (EE) upstream of Tyr and the hydrophobic Phe-Phe-Phe (FFF) downstream precisely match Csk active-site preference (acidic residues N-terminal to Tyr, hydrophobic residues C-terminal), making it more specific for Csk than generic Src substrates (e.g., Srctide). N-terminal 5-FAM allows homogeneous quantification of Tyr8 phosphorylation: (1) chip/capillary mobility-shift assays (Caliper)-phosphorylation adds negative charge, separating substrate from product; (2) TR-FRET/LANCE-a Eu-labeled pan anti-phosphotyrosine (pTyr) antibody undergoes time-resolved FRET with FAM; (3) direct fluorescence-polarization / fluorescence kinase readouts. It is suited to Csk activity assays, IC50 screening of Csk inhibitors and compounds modulating the Csk-Src axis, studies of Src-family autoinhibition/deinhibition, and drug discovery in T-cell activation and tumor migration pathways. Protect from light at all times and prevent phosphatase contamination. | Csk (C-terminal Src kinase) tyrosine kinase assays, Tyr phosphorylation, Csk-optimized specific substrate, homogeneous mobility/MSA assay, TR-FRET/LANCE anti-pTyr, Csk inhibitor screening, Src-family negative regulation (Tyr527 phosphorylation), T-cell receptor signaling, tumor migration drug discovery | Csk (phosphorylates Tyr8; also phosphorylates Src-family C-terminal Tyr527); related kinase TNK1; recognized by Eu-labeled anti-pTyr antibody (TR-FRET); negative regulator of Src-family kinases (c-Src/Fyn/Lck/Lyn etc.) |
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