Cyclotides are head-to-tail backbone cyclized peptides with knotted topology brought about by three conserved disulfide bonds1. Kalata B1 was one of the first cyclotides discovered and is now well-characterized in terms of its structure and activity2. Due to its remarkable stability at high temperature and on exposure to proteases it has been considered as a potential drug scaffold3,4. To date, the most commonly used method for peptide head-to-tail cyclization has been native chemical ligation5. However, enzyme-mediated cyclization has been emerging rapidly in recent years because of several attractive properties, including efficiency, safety and cost-effectiveness. Sortase A is a bacterial enzyme with transpeptidase activity that recognizes the penta amino acid motif “LPXTG” and cleaves the peptide bond between Thr and Gly6 following attack by a poly-glycine sequence resulting in an amide bond formation. Here, we present the cyclization of the disulfide rich kalata B1 by sortase A as a proof of concept of disulfide rich peptide cyclization by enzymes. The successful cyclization of kalata B1 with LPVTG motif in loop 6, its structure and activity will be discussed.
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