Generation of coilr probe peptides for viper-labeling of cellular proteins

Versatile Interacting Peptide (VIP) tags are a new class of genetically-encoded tag designed for imaging cellular proteins by fluorescence and electron microscopy. In 2018, we reported the VIPER tag (Doh et al., 2018), which contains two elements: A genetically-encoded peptide tag (i.e., CoilE) and a probe peptide (i.e., CoilR). These two peptides deliver contrast to a protein of interest by forming a specific, high-Affinity heterodimer. The probe peptide was designed with a single cysteine residue for site-specific modification via thiol-maleimide chemistry. This feature can be used to attach a variety of biophysical reporters to the peptide, including bright fluorophores for fluorescence microscopy or electron-dense nanoparticles for electron microscopy. In this Bio-Protocol, we describe our methods for expressing and purifying recombinant CoilR. Additionally, we describe protocols for making fluorescent or biotinylated probe peptides for labeling CoilE-Tagged cellular proteins. This protocol is complemented by two other Bio-Protocols outlining the use of VIPER (Doh et al., 2019a and 2019b).