Novel post-translational oligomerization of peptidyl dehydrodopa model compound, 1,2-dehydro-N-acetyldopa methyl ester.

Post-translational modification of peptidyl tyrosine to peptidyl dopa is widely observed in different marine organisms. While peptidyl dopas are oxidatively converted to dehydrodopa derivatives, nothing is known about the further fate of dehydrodopyl compounds. To fill this void, we studied the oxidation chemistry of a peptidyl dehydrodopa mimic, 1,2-dehydro-N-acetyldopa methyl ester with mushroom tyrosinase. We employed both routine biochemical studies and reversed phase liquid chromatography mass spectrometry to investigate the course of the reaction. Tyrosinase catalyzed the oxidation of 1,2-dehydro-N-acetyldopa methyl ester readily generating its typical o-quinone as the transient two-electron oxidation product. This quinone was extremely unstable and rapidly reacted with the parent compound forming benzodioxan type oligomeric products. Reaction mixture containing chemically made o-benzoquinone and 1,2-dehydro-N-acetyldopa methyl ester generated a mixed adduct of benzoquinone and 1,2-dehydro-N-acetyldopa methyl ester. Based on this finding, we propose that peptidyl dehydrodopa also exhibits a similar transformation accounting partially for the adhesive and cementing properties of dopyl proteins in nature.