SpyCatcher-NTEV: A Circularly Permuted, Disordered SpyCatcher Variant for Less Trace Ligation

Catcher/Tag Toolbox: Biomolecular Click-Reactions For Protein Engineering Beyond Genetics

Manipulating protein architectures beyond genetic control has attracted widespread attention. Catcher/Tag systems enable highly specific conjugation of proteins in vivo and in vitro via an isopeptide-bond. They provide efficient, robust, and irreversible strategies for protein conjugation and are simple yet powerful tools for a variety of applications in enzyme industry, vaccines, biomaterials, and cellular applications. Here we summarize recent development of the Catcher/Tag toolbox with a particular emphasis on the design of Catcher/Tag pairs targeted for specific applications. We cover the current limitations of the Catcher/Tag systems and discuss the pH sensitivity of the reactions. Finally, we conclude some of the future directions in the development of this versatile protein conjugation method and envision that improved control over inducing the ligation reaction will further broaden the range of applications.

Investigating the effects of cyclic topology on the performance of a plastic degrading enzyme for polyethylene terephthalate degradation

Agitation is a commonly encountered stress for enzymes during all stages of production and application, but investigations that aim to improve their tolerance using topological engineering have yet to be reported. Here, the plastic-degrading enzyme IsPETase was cyclized in a range of topologies including a cyclic monomer, cyclic dimer and catenane using SpyTag/SpyCatcher technologies, and their tolerance towards different stresses including mechanical agitation was investigated. The cyclic dimer and catenane topologies were less susceptible to agitation-induced inactivation resulting in enhancement of polyethylene terephthalate (PET) degradation. While contrary to conventional belief, cyclic topologies did not improve tolerance of IsPETase towards heat or proteolytic treatment, the close proximity of active sites in the dimeric and catenane variants was found to enhance PET conversion into small soluble products. Together, these findings illustrate that it is worthwhile to explore the topology engineering of enzymes used in heterogeneous catalysis as it improves factors that are often overlooked in homogeneous catalysis studies.

DogCatcher allows loop-friendly protein-protein ligation

There are many efficient ways to connect proteins at termini. However, connecting at a loop is difficult because of lower flexibility and variable environment. Here, we have developed DogCatcher, a protein that forms a spontaneous isopeptide bond with DogTag peptide. DogTag/DogCatcher was generated initially by splitting a Streptococcus pneumoniae adhesin. We optimized DogTag/DogCatcher through rational design and evolution, increasing reaction rate by 250-fold and establishing millimolar solubility of DogCatcher. When fused to a protein terminus, DogTag/DogCatcher reacts slower than SpyTag003/SpyCatcher003. However, inserted in loops of a fluorescent protein or enzyme, DogTag reacts much faster than SpyTag003. Like many membrane proteins, the ion channel TRPC5 has no surface-exposed termini. DogTag in a TRPC5 extracellular loop allowed normal calcium flux and specific covalent labeling on cells in 1 min. DogTag/DogCatcher reacts under diverse conditions, at nanomolar concentrations, and to 98% conversion. Loop-friendly ligation should expand the toolbox for creating protein architectures.

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Spontaneous transamidation at internal sites harnessing a DogTag/DogCatcher pair

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DogCatcher is designed and bred for high solubility and rapid reaction

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Within protein loops DogTag can clamp on its partner faster than SpyTag003

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Fast and faithful fluorescent labeling of an ion channel at the cell surface via DogTag

Development of SpyTag/SpyCatcher-Bacmid Expression Vector System (SpyBEVS) for Protein Bioconjugations Inside of Silkworms

Protein conjugations at post-translational levels are known to be essential to protein stability and function. Recently, it has been proven that the split protein CnaB2 (SpyTag/SpyCatcher, ST/SC) from Streptococcus pyogenes can induce covalent conjugation rapidly and efficiently under various conditions. The protein of interest fused with the split protein SC/ST could be assembled spontaneously. In light of this finding, we introduced the ST/SC protein coupling concept into the silkworm-bacmid protein expression system (SpyBEVS). As a proof of concept, we first examined and confirmed that a competent ligation occurred between ST/SC-fused protein partners in vitro in cultured silkworm cells and in vivo in silkworm larvae by co-infection of several recombinant baculoviruses. The protein conjugation could be also achieved sufficiently by a simple one-step mixture of purified ST/SC-tagged peptide-protein pairs in vitro. Given the flexibility and robustness of silkworm-BEVS, our results on SpyBEVS show an alternative method for enabling the production of protein decorations in vitro and inside of silkworms.

Pick a Tag and Explore the Functions of Your Pet Protein

Protein tags have been essential for advancing our knowledge of the function of proteins, their localization, and the mapping of their interaction partners. Expressing epitope-tagged proteins has become a standard practice in every life science laboratory and, thus, continues to enable new studies. In recent years, several new tagging moieties have entered the limelight, many of them bringing new functionalities, such as targeted protein degradation, accurate quantification, and proximity labeling. Other novel tags aim at tackling research questions in challenging niches. In this review, we elaborate on recently introduced tags and the opportunities they provide for future research endeavors. In addition, we highlight how the genome-engineering revolution may boost the field of protein tags.

An Intrinsically Disordered Peptide-Peptide Stapler for Highly Efficient Protein Ligation Both in Vivo and in Vitro

Herein, we report an intrinsically disordered protein SpyStapler that can catalyze the isopeptide bond formation between two peptide tags, that is, SpyTag and BDTag, both in vitro and in vivo. SpyStapler and BDTag are developed by splitting SpyCatcher-the cognate protein partner of SpyTag-at the more solvent exposed second loop region. Regardless of their locations in protein constructs, SpyStapler enables efficient covalent coupling of SpyTag and BDTag under a variety of mild conditions in vitro (yield ∼80%). Co-expression of SpyStapler with telechelic dihydrofolate reductase (DHFR) bearing a SpyTag at N-terminus and a BDTag at C-terminus leads to direct cellular synthesis of a circular DHFR. Mechanistic studies involving circular dichroism and nuclear magnetic resonance spectrometry reveal that SpyStapler alone is disordered in solution and forms a stable folded structure ( T_m ∼ 55 °C) in the presence of both SpyTag and BDTag upon isopeptide bonding. No ordered structure can be formed in the absence of either tag. The catalytically inactive SpyStapler-EQ mutant cannot form a stable physical complex with SpyTag and BDTag, but it can fold into ordered structure in the presence of the ligated product (SpyTag-BDTag). It suggests that the isopeptide bond is important in stabilizing the complex. Given its efficiency, resilience, and robustness, SpyStapler provides new opportunities for bioconjugation and creation of complex protein architectures.

Controlling SpyTag/SpyCatcher Reactivity via Redox-Gated Conformational Restriction

Herein, we report that the reactivity of genetically encoded SpyTag/SpyCatcher chemistry can be manipulated via redox-gated conformational restriction, which facilitates the preparation of all-protein-based hydrogel with latent reactive sites for subsequent covalent functionalization.