Abstract:
:The multifunctional polypeptide cyclosporin synthetase (CySyn) remains one of the most complex nonribosomal peptide synthetase described. In this study we used a highly specific photoaffinity labeling procedure with the natural cofactor S-adenosyl-L-methionine (AdoMet), 14C-isotopically labeled at the Sdelta methyl group to probe the concerted AdoMet-binding interaction of the N-methyltransferase (N-MTase) centers of CySyn. The binding stoichiometry for the enzyme-AdoMet complex was determined to be 1:7, which is in agreement with inferences made from analysis of the complementary DNA sequence of the simA gene encoding the CySyn polypeptide. The photolabeling of the AdoMet-binding sites displayed homotropic negative cooperativity, characterized by a curvilinear Scatchard plot with upward concavity. Although, the process of N-methyl transfer is not a critical event for peptide elongation, the destabilizing homotropic interactions between N-MTase centers that were observed may represent a mechanism whereby the enzyme preserves the proficiency of the substrate-channeling process of cyclosporin peptide assembly over a broad range of cofactor concentrations. Furthermore, we demonstrated the utility of the photolabeling procedure for tracking the enzyme during purification.
journal_name
Photochem Photobioljournal_title
Photochemistry and photobiologyauthors
Velkov T,Lawen Adoi
10.1562/0031-8655(2003)077<0129:plotnm>2.0.co;2subject
Has Abstractpub_date
2003-02-01 00:00:00pages
129-37issue
2eissn
0031-8655issn
1751-1097journal_volume
77pub_type
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