In vitro biosynthesis of ring-extended cyclosporins

Cyclosporin synthetase, a multifunctional polypeptide, catalyses the biosynthesis of the set of natural cyclosporins. We report that this enzyme is also capable of introducing β-alanine into position 7 or 8 of the ring instead of the α-alanines present at these positions in cyclosporin A. This leads to 34-membered rings in contrast to the 33-membered ring of the cycloundecapeptide cyclosporin A. Both [βAla⁷]CyA and [βAla⁸](CyA show immunosuppressive activity. The cyclosporin synthetase-related enzyme peptolide SDZ 214-103 synthetase, on the other hand, does not incorporate either β-alanine into position 7 or β-hydroxy acids into position 8, confirming the previously described higher substrate specificity of this enzyme compared with cyclosporin synthetase