Search

A technique combining ion mobility spectrometry‐mass spectrometry (IMS‐MS) and supercharging electrospray ionization (ESI) has been demonstrated to differentiate protein chemical topology effectively. Incorporating as many charges as possible into proteins via supercharging ESI allows the protein chains to be largely unfolded and stretched, revealing their hidden chemical topology. Different chemical topologies result in differing geometrical sizes of the unfolded proteins due to constraints in torsional rotations in cyclic domains. By introducing new topological indices, such as the chain‐length‐normalized collision cross‐section (CCS) and the maximum charge state (zM) in the extensively unfolded state, we were able to successfully differentiate various protein chemical topologies, including linear chains, ring‐containing topologies (lasso, tadpole, multicyclics, etc.), and mechanically interlocked rings, like catenanes. [ABSTRACT FROM AUTHOR]

Entangled proteins have attracted significant research interest. Herein, we report the first rationally designed lasso proteins, or protein [1]rotaxanes, by using a p53dim‐entwined dimer for intramolecular entanglement and a SpyTag‐SpyCatcher reaction for side‐chain ring closure. The lasso structures were confirmed by proteolytic digestion, mutation, NMR spectrometry, and controlled ligation. Their dynamic properties were probed by experiments such as end‐capping, proteolytic digestion, and heating/cooling. As a versatile topological intermediate, a lasso protein could be converted to a rotaxane, a heterocatenane, and a "slide‐ring" network. Being entirely genetically encoded, this robust and modular lasso‐protein motif is a valuable addition to the topological protein repertoire and a promising candidate for protein‐based biomaterials. [ABSTRACT FROM AUTHOR]

Herein, we report the biosynthesis of protein heterocatenanes using a programmed sequence of multiple post‐translational processing events including intramolecular chain entanglement, in situ backbone cleavage, and spontaneous cyclization. The approach is general, autonomous, and can obviate the need for any additional enzymes. The catenane topology was convincingly proven using a combination of SDS‐PAGE, LC‐MS, size exclusion chromatography, controlled proteolytic digestion, and protein crystallography. The X‐ray crystal structure clearly shows two mechanically interlocked protein rings with intact folded domains. It opens new avenues in the nascent field of protein‐topology engineering. [ABSTRACT FROM AUTHOR]