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.     

Biodegradable silk-curcumin composite for sustained drug release and visual wound monitoring

The production of biodegradable dressing capable of sustained drug release, along with the monitoring of wound conditions, represents new heights of multifunctional platforms for wound care. The reported curcumin-loaded silk fibroin has shown sustained drug release over the time of 10 days through a non-Fickian diffusion process satisfying Korsmeyer-Peppas' model along with the visual monitoring of wound healing through notable color variation with pH as a biomarker. The superhydrophobic nature (water contact angle = 163.7) of the SF, along with the lipophilicity (CA = 0 (Blood)) and hygroscopic nature prevents wetting of wound surface, whereas the excess exudates from wounds are absorbed along with sufficient water and oxygen permeability. The pH responsiveness as a result of the keto-enol tautomerism in curcumin was utilized for wound monitoring through visual indication enabling even ordinary people to detect the state of the wound. The in-situ biodegradation studies verified using cow-dung slurry, the degradability of the material with 25.3% weight loss within 30 days following first-order kinetics (R² = 0.994), as a result of the attack of proteolytic enzymes on the amino acid units of SF, mitigating the concerns of medical wastes.