Fluorescent Peptide Toxin for Selective Visualization of the Voltage-Gated Potassium Channel KV1.3

Upregulation of the voltage-gated potassium channel K(V)1.3 is implicated in a range of autoimmune and neuroinflammatory diseases, including rheumatoid arthritis, psoriasis, multiple sclerosis, and type I diabetes. Understanding the expression, localization, and trafficking of K(V)1.3 in normal and disease states is key to developing targeted immunomodulatory therapies. HsTX1[R14A], an analogue of a 34-residue peptide toxin from the scorpion Heterometrus spinifer, binds K(V)1.3 with high affinity (IC50 of 45 pM) and selectivity (2000-fold for K(V)1.3 over K(V)1.1). We have synthesized a fluorescent analogue of HsTX1[R14A] by N-terminal conjugation of a Cy5 tag. Electrophysiology assays show that Cy5-HsTX1[R14A] retains activity against K(V)1.3 (IC50 similar to 0.9 nM) and selectivity over a range of other potassium channels (K(V)1.2, K(V)1.4, K(V)1.5, K(V)1.6, K(Ca)1.1 and K(Ca)3.1), as well as selectivity against heteromeric channels assembled from K(V)1.3/K(V)1.5 tandem dimers. Live imaging of CHO cells expressing green fluorescent protein-tagged K(V)1.3 shows co-localization of Cy5-HsTX1[R14A] and K(V)1.3 fluorescence signals at the cell membrane. Moreover, flow cytometry demonstrated that Cy5-HsTX1[R14A] can detect K(V)1.3-expressing CHO cells. Stimulation of mouse microglia by lipopolysaccharide, which enhances membrane expression of K(V)1.3, was associated with increased staining by Cy5-HsTX1[R14A], demonstrating that it can be used to identify K(V)1.3 in disease-relevant models of inflammation. Furthermore, the biodistribution of Cy5-HsTX1[R14A] could be monitored using ex vivo fluorescence imaging of organs in mice dosed subcutaneously with the peptide. These results illustrate the utility of Cy5-HsTX1[R14A] as a tool for visualizing K(V)1.3, with broad applicability in fundamental investigations of K(V)1.3 biology, and the validation of novel disease indications where K(V)1.3 inhibition may be of therapeutic value.

Automated summary

Upregulation of the voltage-gated potassium channel K(V)1.3 is associated with autoimmune and neuroinflammatory diseases. A peptide analogue called HsTX1[R14A] has high affinity for K(V)1.3 and can be visualized using fluorescence imaging. This research is significant for understanding the biology of K(V)1.3 and developing treatments for related diseases.