Chemical Topology and Complexity of Protein Architectures.

Chemical topology has emerged as one intriguing feature in protein engineering. Nature demonstrates the elegance and power of protein topology engineering in the unique biofunctions and exceptional stabilities of cyclotides and lasso peptides. With entangling protein motifs and genetically encoded peptide-protein chemistry, artificial proteins with complex topologies, including cyclic proteins, star proteins, and protein catenanes, have become accessible. Among them, proteins with mechanical bonds ('mechanoproteins') are of special interest, owing to their potential functional benefits such as structure stabilization, quaternary structure control, synergistic multivalency effect, and dynamic mechanical sliding/switching properties. In this review article, we summarize recent progress in the field of protein topology engineering as well as the challenges and opportunities that it holds.