Studies on the Mechanism of Allergic Contact Dermatitis: The Reaction of α-Methylene-γ-Butyrolactone with Peptide-Bound Lysine

Abstract

The binding of low-molecular-weight compounds to nucleophilic side-chains of amino acids bound within a protein, resulting in a hapten-modified macromolecule, is discussed to represent the very first step within the development of allergic contact dermatitis. For one of the best-known occupational dermatoses in the field of plant breeding, the so-called tulip fingers, α-methylene-γ-butyrolactone (tulipalin A) was proved to be the causative agent. In this paper, the reaction of tulipalin A with Nα-hippuryl-L-lysine as a model for peptide-bound lysine was studied. After the incubation of the α-methylene-γ-butyrolactone with the dipeptide in varying molar ratios in methanolic solution at 37°C up to 3 weeks, the reaction was monitored using reversed-phase high-performance liquid chromatography with UV detection. Tulipalin A was found to react with the Ε-amino group, resulting in the formation of one characteristic reaction product. After isolation, the structure of this addition product was unambiguously characterised by nuclear magnetic resonance spectroscopy as 2-(2-benzoylamino-acetylamino)-6-[(2-oxo-tetrahydro-furan-3-ylmethyl)amino] hexanoic acid (Hip-LysTu). After incubation of bovine serum albumin with tulipalin A, followed by acid hydrolysis and amino acid analysis, LysTu was found as addition product, thus representing the first known amino acid derivative resulting from the conjugation of the electrophilic α-methylene-γ-butyrolactone to protein.