AlbuCatcher for Long-Acting Therapeutics

Therapeutic proteins, pivotal for treating diverse human diseases due to their biocompatibility and high selectivity, often face challenges such as rapid serum clearance, enzymatic degradation, and immune responses. To address these issues and enable prolonged therapeutic efficacy, techniques to extend the serum half-life of therapeutic proteins are crucial. The AlbuCatcher, a conjugate of human serum albumin (HSA) and SpyCatcher, was proposed as a general technique to extend the serum half-life of diverse therapeutic proteins. HSA, the most abundant blood protein, exhibits a long intrinsic half-life through Fc receptor (FcRn)-mediated recycling. The SpyTag/SpyCatcher (ST/SC) system, known for forming irreversible isopeptide bonds, was employed to conjugate HSA and therapeutic proteins. Site-specific HSA conjugation to SC was achieved using an inverse electron-demand Diels-Alder (IEDDA) reaction, minimizing activity loss. Using urate oxidase (Uox) as a model protein with a short half-life, the small ST was fused to generate Uox-ST. Then, HSA-conjugated Uox (Uox-HSA) was successfully prepared via the Uox-ST/AlbuCatcher reaction. In vitro enzyme assays demonstrated that the impact of ST fusion and HSA conjugation on Uox enzymatic activity is negligible. Pharmacokinetics studies in mice revealed that Uox-HSA exhibits a significantly longer serum half-life (about 18 h) compared to Uox-WT (about 2 h). This extended half-life is attributed to FcRn-mediated recycling of HSA-conjugated Uox, demonstrating the effectiveness of the AlbuCatcher strategy in enhancing the pharmacokinetics of therapeutic proteins.

Biomolecular Click Reactions Using a Minimal pH-Activated Catcher/Tag Pair for Producing Native-Sized Spider-Silk Proteins

A type of protein/peptide pair known as Catcher/Tag pair spontaneously forms an intermolecular isopeptide bond which can be applied for biomolecular click reactions. Covalent protein conjugation using Catcher/Tag pairs has turned out to be a valuable tool in biotechnology and biomedicines, but it is essential to increase the current toolbox of orthogonal Catcher/Tag pairs to expand the range of applications further, for example, for controlled multiple-fragment ligation. We report here the engineering of novel Catcher/Tag pairs for protein ligation, aided by a crystal structure of a minimal CnaB domain from Lactobacillus plantarum. We show that a newly engineered pair, called SilkCatcher/Tag enables efficient pH-inducible protein ligation in addition to being compatible with the widely used SpyCatcher/Tag pair. Finally, we demonstrate the use of the SilkCatcher/Tag pair in the production of native-sized highly repetitive spider-silk-like proteins with >90 % purity, which is not possible by traditional recombinant production methods.

Intramolecular covalent bonds in Gram-positive bacterial surface proteins

Gram-positive bacteria experience considerable mechanical perturbation when adhering to host surfaces during colonization and infection. They have evolved various adhesion proteins that are mechanically robust to ensure strong surface adhesion. Recently, it was discovered that these adhesion proteins contain rare, extra intramolecular covalent bonds that stabilize protein structures and participate in surface bonding. These intramolecular covalent bonds include isopeptides, thioesters, and ester bonds, which often form spontaneously without the need for additional enzymes. With the development of single-molecule force spectroscopy techniques, the detailed mechanical roles of these intramolecular covalent bonds have been revealed. In this review, we summarize the recent advances in this area of research, focusing on the link between the mechanical stability and function of these covalent bonds in Gram-positive bacterial surface proteins. We also highlight the potential impact of these discoveries on the development of novel antibiotics and chemical biology tools.

Engineering a Blue Light Inducible SpyTag System (BLISS)

The SpyCatcher/SpyTag protein conjugation system has recently exploded in popularity due to its fast kinetics and high yield under biologically favorable conditions in both in vitro and intracellular settings. The utility of this system could be expanded by introducing the ability to spatially and temporally control the conjugation event. Taking inspiration from photoreceptor proteins in nature, we designed a method to integrate light dependency into the protein conjugation reaction. The light-oxygen-voltage domain 2 of Avena sativa (AsLOV2) undergoes a dramatic conformational change in its c-terminal Jα-helix in response to blue light. By inserting SpyTag into the different locations of the Jα-helix, we created a blue light inducible SpyTag system (BLISS). In this design, the SpyTag is blocked from reacting with the SpyCatcher in the dark, but upon irradiation with blue light, the Jα-helix of the AsLOV2 undocks to expose the SpyTag. We tested several insertion sites and characterized the kinetics. We found three variants with dynamic ranges over 15, which were active within different concentration ranges. These could be tuned using SpyCatcher variants with different reaction kinetics. Further, the reaction could be instantaneously quenched by removing light. We demonstrated the spatial aspect of this light control mechanism through photopatterning of two fluorescent proteins. This system offers opportunities for many other biofabrication and optogenetics applications.

Multivalent-Interaction-Driven Assembly of Discrete, Flexible, and Asymmetric Supramolecular Protein Nano-Prisms

Current approaches to design monodisperse protein assemblies require rigid, tight, and symmetric interactions between oligomeric protein units. Herein, we introduce a new multivalent-interaction-driven assembly strategy that allows flexible, spaced, and asymmetric assembly between protein oligomers. We discovered that two polygonal protein oligomers (ranging from triangle to hexagon) dominantly form a discrete and stable two-layered protein prism nanostructure via multivalent interactions between fused binding pairs. We demonstrated that protein nano-prisms with long flexible peptide linkers (over 80 amino acids) between protein oligomer layers could be discretely formed. Oligomers with different structures could also be monodispersely assembled into two-layered but asymmetric protein nano-prisms. Furthermore, producing higher-order architectures with multiple oligomer layers, for example, 3-layered nano-prisms or nanotubes, was also feasible.