Distinct 3-disulfide-bonded isomers of tridegin differentially inhibit coagulation factor XIIIa: The influence of structural stability on bioactivity

NMR-Based Structural Characterization of a Two-Disulfide-Bonded Analogue of the FXIIIa Inhibitor Tridegin: New Insights into Structure–Activity Relationships

“…Therefore, it can be assumed for the disulfide bond Cys19-Cys25 in the three-disulfide-bonded tridegin isomer that it is generated after the formation of the secondary structure elements within the folding process. With regard to the structure-activity relationships, it can be assumed that the low structural influence of the disulfide bond results in an already experimentally described comparable binding behavior and inhibitory potential to FXIIIa for the three-disulfide-bonded isomer B [28] and the two-disulfide-bonded isomer B [C19S,C25S] [29].…”

“…In addition, activity studies of the N-terminal fragment on FXIIIa were performed using the established FXIIIa isopeptidase activity assay [28][29][30]. As already observed in the case of a three-disulfide-bonded N-terminal fragment of tridegin [30], no inhibitory potential against FXIIIa was found.…”

“…Tridegin belongs to the class of cysteine-rich peptides due to its 6 cysteines within the amino acid sequence. The natural disulfide bond connectivity of tridegin could not be elucidated so far [28][29][30][31], which is due to the fact that a peptide with 6 cysteines has the ability to form 15 different three-disulfide-bonded isomers. So far, final conclusions have not been drawn concerning the folding of tridegin to the bioactive conformation and whether it is folded in a BPTI-like (Bovine pancreatic trypsin inhibitor) fashion, according to which one isomer is preferentially formed, or in a hirudin-like manner, where a maximum of 15 possible three-disulfide-bonded isomers are formed [32,33].…”

“…A folding experiment performed by Böhm et al in 2014 provided first hints regarding the preferentially formed disulfide-bonded isomers of tridegin [30]. Therein, three of the 15 possible three-disulfide-bonded isomers were identified, which all shared the disulfide bond between Cys19-Cys25 and possessed similar activities toward FXIIIa [28,30]. In addition to the three-disulfide-bonded tridegin isomers, several variants lacking the disulfide bond between Cys19-Cys25 were synthesized in a following approach in order to determine the significance of this bond for their inhibitory potential against FXIIIa [29].…”

Importance of the Cyclic Cystine Knot Structural Motif for Immunosuppressive Effects of Cyclotides

“…32,33 The CCK is an essential attribute for the structure of cyclotides, but little is known about its role on bioactivity. 22,34,35 The current study explores the functional role of the CCK motif using the kalata B1 analog, and clinical drug candidate T20K, as a prototypical cyclotide. Several partly reduced or wrongly formed cystine knot variants were prepared by chemical synthesis and were assayed for antiproliferative activity on peripheral blood mononuclear cells (PBMCs) relative to the native folded peptide.…”