| Popis: |
The molecular and functional diversification conferred by posttranslational modification (PTM) of proteins is a common target and source of inspiration for chemical biologists. For example, the formylglycine-generating enzyme (FGE)—a copper-based oxidase— transforms the thiol group of cysteine residues into an aldehyde group, which is required for sulfatase activity and can serve as a bioconjugation handle in protein engineering applications. In the late 1970s, long before formylglycine residues were identified as biologically relevant, Lowe demonstrated that photolysis of an α-thioarylketone derivative of the active-site cysteine residue of papain followed by NaBH4 reduction gave the serine derivative, presumably via thioaldehyde and formylglycine intermediates. We decided to reinvestigate this potentially useful transformation, which at the outset was both inefficient and poorly characterized. We found that photolysis of α-thioarylketone derivatives of simple cysteine peptides with electron-donating aromatic substituents, like those used by Lowe, leads to predominant β-elimination, where the resulting thiyl radicals combine to form disulfides. However, guided by the photochemistry work of Wagner, we found that those derivatives bearing electron-withdrawing groups lead to high quantum yields of the desired Norrish Type II processes, which lead to mixtures of cysteine enethiolate, a tautomeric derivative of the thioaldehyde, and isothiazolones. The enethiolates, which were stable with respect to hydrolysis, could be converted into isothiazolones through the addition of an oxidant (DTNB), and vice versa through the addition of a reductant (TCEP). Hydrolysis of the thioaldehyde/enethiol to give formylglycine was only observed for cysteine residues embedded within certain peptide sequences, such as those found in sulfatases, the target of FGE. To conclude, our investigation has both identified an efficient small-molecule mimic of FGE and furthered our understanding of this important enzyme. 2025-04-14 |
