Biogenesis of the Thio-Ether Bond and other Processing Events

Biogenesis of the Thio-Ether Bond and Other Processing Events 

The identification of a thio-ether bond in the active site of GOase (Ito et al., 1991) immediately encouraged speculation about its biogenesis. Is the formation of this bond autocatalytic as appears to be the case with the TPQ cofactor in amine oxidases (Dooley, 1999) or does it require chaperones as is the case in the biogenesis of the TTQ cofactor (Christoserdov et al., 1991) Does biogenesis of the thioether bond involve radicals There are 

Under rigorous eopper-depleted eonditions, the dominant GOase species produced is Form I and this has been isolated and purified. Aerobic incubation of Form I with Cu leads to its eonversion to Form III, the visible spectrum showing this to be the aetivated form with the thioether bond formed. Incubation of Form I with Cu under anaerobic conditions gives a species with the same eireular diehroism speetrum as inaetive wild type indicating that copper has been ineorporated into the protein as Cu.  

A large number of eopper/phenoxide complexes have been prepared as models for GOase. Several early studies were eomplieated by the formation of phenoxide-bridged dimeric complexes, which affects the solution chemistry of these compounds (Whittaker et al., 1996a Zurita et al., 1996 Itoh et al., 1997). Latterly, however, several groups have succeeded in cleanly isolating monomeric square pyramidal copper (II)/phenoxide complexes, from which copper(II)/phenoxyl species can be accessed by reversible, one-electron oxidation (Halfen et al., 1997 Zurita et al., 1997  

FIGURE 6. A structural model compound for galactose oxidase that forms a phenoxyl species closely resembling the oxidised form of the enzyme (Halcrow et al., 1998). 

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