Hansen PR, Flyge H, Holm A, Lauritzen E, Larsen BD. Photochemical conjugation of peptides to carrier proteins using 1,2,3-thiadiazole-4-carboxylic acid. Immunoreactivity of free C-terminal epitope with specific antibodies.
INTERNATIONAL JOURNAL OF PEPTIDE AND PROTEIN RESEARCH 1996;
47:419-26. [PMID:
8836769 DOI:
10.1111/j.1399-3011.1996.tb01092.x]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A new heterobifunctional cross-linking reagent, 1,2,3-thiadiazole-4-carboxylic acid, for the photochemical conjugation of peptides to proteins is described. The title compound can be coupled directly to a protected peptide resin during solid-phase peptide synthesis (SPPS) using standard coupling procedures. The probe is stable to TFA deprotection/cleavage mixtures containing ethanedithiol commonly used in Fmoc-SPPS. Furthermore, tritium may easily be introduced into the thiadiazole ring by base-catalyzed hydrogen-exchange. Upon irradiation at 245-300 nm, parent 1,2,3-thiadiazole rapidly eliminates N2, generating very reactive thioketene which reacts with amines to give a thioamide in high yield, even when the photolysis is carried out in hydroxylic solvents. In order to investigate the potential of the title compound as a heterobifunctional cross-linking reagent a model study with angiotensin II (AII) was conducted. The photoreactive peptide N2-4-carbonyl-1,2,3-thiadiazole-AII (TDA-AII) was synthesized by Fmoc-SPPS and conjugated to bovine serum albumin (BSA) by photolysis at 245 and 300 nm. By use of a capture competition ELISA, the C-terminal Pro-Phe epitope of photoconjugated AII with the sequence DRVYIHPF was shown to bind specifically to antiAII antibodies (anti-AII abs), although antibodies against both the C- and N-terminal epitopes were present in the assay. A dipeptide His-Leu carboxy-extension form of AII, angiotensin I (AI), only bound to anti-AII abs at 100-200 times higher concentrations, showing that the C-terminal epitope was blocked by the dipeptide.
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