Crystal structure of the precursor of galactose oxidase: An unusual self-processing enzyme

Galactose oxidase (EC 1.1.3.9) is a monomeric enzyme that contains a single copper ion and catalyses the stereospecific oxidation of primary alcohols to their corresponding aldehydes. The protein contains an unusual covalent thioether bond between a tyrosine, which acts as a radical center during th e two-electron reaction, and a cysteine. The enzyme is produced in a precur sor form lacking the thioether bond and also possessing an additional 17-aa prosequence at the N terminus. Previous work has shown that the aerobic ad dition of Cu2+ to the precursor is sufficient to generate fully processed m ature enzyme. The structure of the precursor protein has been determined to 1.4 Angstrom, revealing the location of the pro-sequence and identifying s tructural differences between the precursor and the mature protein. Structu ral alignment of the precursor and mature forms of galactose oxidase shows that five regions of main chain and some key residues of the active site di ffer significantly between the two forms. The precursor structure provides a starting point for modeling the chemistry of thioether bond formation and pro-sequence cleavage.