LAUSR

The interplay between protein folding and chemical reaction has been an intriguing subject. In this contribution, we report the study of SpyTag and SpyCatcher reactive mutants using combined techniques of SDS-PAGE, LC-MS, circular dichroism, and NMR spectroscopy. It was found that the wild-type SpyCatcher is well-folded in solution and docks with SpyTag to form an intermediate that promotes isopeptide formation. By contrast, the double mutant SpyCatcherVA is disordered in solution, yet remains reactive toward SpyTag, forming a well-folded covalent complex. Control experiments using the catalytically inactive mutants further reveal the critical role of the isopeptide bond in stabilizing the otherwise loose SpyTag-SpyCatcherVA complex, amplifying the effect of minute sequence disparity. We believe that the synergy between protein folding and isopeptide bonding is an effective way to enhance protein stability and engineer protein-protein interactions.