The UniOne® Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay Kit is used for evaluating the binding activity of human CDK6 and CRBN-mediated PROTAC.

Proteolysis-targeting chimeras (PROTACs) utilize their bifunctional molecular structure to simultaneously bind target proteins and substrate-recognition subunits of E3 ubiquitin ligase complexes, inducing the formation of ternary complexes that trigger ubiquitination and proteasomal degradation of the target protein. This mechanism differs from the binary binding mode of traditional small-molecule inhibitors, making the efficacy evaluation of PROTACs highly dependent on direct detection of ternary complex formation. Time-resolved fluorescence resonance energy transfer (TR-FRET) technology, with its homogeneous, wash-free, and high-sensitivity characteristics, has become the preferred method for studying PROTAC-mediated target protein-E3 ligase interactions. The core of this technology lies in the energy transfer between long-lived fluorescent donors (e.g., europium or terbium complexes) and suitable acceptor molecules. When the donor and acceptor are brought into nanometer-scale proximity due to specific biomolecular interactions, the donor can transfer energy to the acceptor via non-radiative means, causing the latter to emit characteristic long-lived fluorescence. By employing a time-resolved detection mode to delay signal reading, background fluorescence interference is effectively eliminated, thereby improving the signal-to-noise ratio and specificity of the assay.

For evaluating the activity of cyclin-dependent kinase 6 (CDK6) and CRBN-mediated PROTACs, UniOne® TR-FRET Human CDK6/CRBN PROTAC Binding Kit is provided. The kit design incorporates validated TR-FRET PROTAC detection strategies, where labeled antibodies recognize differently tagged target proteins and E3 ligase components, forming a donor-target protein-PROTAC-E3 ligase-acceptor complex in the presence of PROTAC molecules. In this system, the donor fluorophore is typically conjugated to an antibody recognizing CDK6 tags (e.g., His-tag), while the acceptor fluorophore is conjugated to an antibody recognizing CRBN tags (e.g., FLAG-tag). When CDK6, PROTAC, and CRBN bind to form a ternary complex, the donor and acceptor are brought into proximity, generating quantifiable TR-FRET signals. The signal intensity correlates positively with the amount of ternary complex formed, serving as direct evidence for assessing PROTAC binding activity. Additionally, the kit may employ a competitive binding mode using fluorescently labeled known ligands, evaluating the binding ability of test PROTACs or ligands to CRBN by monitoring signal reduction. The reaction is performed in microplates with a simple workflow: reagents and test samples are mixed, incubated, and read without complex separation or washing steps.

CDK6, a member of the serine/threonine protein kinase family, regulates the cell cycle transition from G1 to S phase upon binding to cyclin D3. Its dysfunction is closely associated with the development of various cancers. CRBN is the substrate-recognition receptor of the CUL4-RBX1-DDB1 E3 ubiquitin ligase complex, mediating the ubiquitination and degradation of multiple proteins. As CRBN can be bound by immunomodulatory drugs (e.g., lenalidomide), it has become one of the most widely used E3 ligases in PROTAC technology. CDK6-targeting PROTAC molecules simultaneously bind CDK6 and CRBN, leveraging CRBN's E3 ligase activity to induce selective degradation of CDK6, offering a potential therapeutic strategy beyond traditional kinase inhibitors for cancer treatment.

The UniOne® TR-FRET Human CDK6/CRBN PROTAC Binding Kit is primarily used for high-throughput screening and structure-activity relationship studies of PROTAC molecules. By detecting ternary complex formation induced by PROTACs at varying concentrations, a characteristic bell-shaped dose-response curve can be plotted. The concentration corresponding to the peak signal represents the optimal concentration for maximal PROTAC efficacy, a parameter commonly used to rank and prioritize PROTAC molecules. The kit can also evaluate the competitive inhibitory activity of test compounds against CDK6 or CRBN ligand-binding sites. Performance validation typically includes: dose-dependent signal increases induced by positive controls (e.g., known active PROTACs such as BSJ-03-204), negligible signal responses from negative controls (e.g., non-PROTAC ligands), and competitive experiments confirming signal specificity.

In summary, the UniOne® TR-FRET Human CDK6/CRBN PROTAC Binding Kit, based on time-resolved fluorescence resonance energy transfer technology, provides a homogeneous, sensitive, and reliable tool for evaluating the binding activity of PROTAC molecules targeting CDK6 and CRBN. The kit generates specific signals via donor-acceptor fluorophore proximity effects in PROTAC-induced ternary complexes, making it suitable for PROTAC screening, optimization, and activity comparison. It serves as a vital asset in advancing drug discovery in the targeted protein degradation field.