ENZYMATIC BIOSYNTHESIS OF CYCLOSPORINE-A AND ANALOGS

The final assembly of the undecapeptide chain of cyclosporin A and its cyclization is accomplished in Beauveria nivea by cyclosporin synthetase. This multienzyme is the largest integrated enzyme structure so far reported. It has been estimated at approximately 1 400 kDa by two different methods: 1), by 3% SDS-PAGE using die related multienzymes ACV synthetase and gramicidin S synthetase 2 as references (420 and 556 kDa, respectively); and 2), by CsCl density gradient centrifugation experiments using fluorescence-labeled cyclosporin synthetase. Besides cyclosporin A and a number of cyclosporins known from fermentation studies cyclosporin synthetase is capable of synthesizing some new cyclosporins which are so far unobtainable by fermentation. So, for example the synthesis of [N-methyl-(+)-2-amino-3-hydroxy-4,4-dimethyloctanoic acid1]CyA, dihydro-CyA, [L-norvaline2,5, N-methyl-L-norvaline11]CyA, [L-allo-isoleucine5, N-methyl-L-allo-isoleucine11]CyA, [D-2-aminobutyric acid8]CyA, [beta-chloro-D-alanine8]CyA and some related compounds could be established. By using a related but different enzyme from Cylindrotrichum Bonorden, the peptolide [L-threonine2, L-leucine5,10, D-2-hydroxyisovaleric acid8]CyA could be synthesized in vitro. We were able to synthesize these cyclosporins in sufficient quantities to examine their structure by FAB mass spectroscopy and explore their immunosuppressivity. It was found that all new cyclosporins so far synthesized in the in vitro system are immunosuppressive.