Download MendeleyCross-Link Formation of the Cysteine 228-Tyrosine 272 Catalytic Cofactor of Galactose Oxidase Does not Require Dioxygen.
Rogers, M.S., Hurtado-Guerrero, R., Firbank, S.J., Halcrow, M.A., Dooley, D.M., Phillips, S.E.V., Knowles, P.F., McPherson, M.J.(2008) Biochemistry 47: 10428
- PubMed: 18771294
- DOI: https://doi.org/10.1021/bi8010835
- Primary Citation of Related Structures:
2VZ1, 2VZ3 - PubMed Abstract:
Galactose oxidase (GO) belongs to a class of proteins that self-catalyze assembly of their redox-active cofactors from active site amino acids. Generation of enzymatically active GO appears to require at least four sequential post-translational modifications: cleavage of a secretion signal sequence, copper-dependent cleavage of an N-terminal pro sequence, copper-dependent formation of a C228-Y272 thioether bond, and generation of the Y272 radical. The last two processes were investigated using a truncated protein (termed premat-GO) lacking the pro sequence and purified under copper-free conditions. Reactions of premat-GO with Cu(II) were investigated using optical, EPR, and resonance Raman spectroscopy, SDS-PAGE, and X-ray crystallography. Premat-GO reacted anaerobically with excess Cu(II) to efficiently form the thioether bond but not the Y272 radical. A potential C228-copper coordinated intermediate (lambda max = 406 nm) in the processing reaction, which had not yet formed the C228-Y272 cross-link, was identified from the absorption spectrum. A copper-thiolate protein complex, with copper coordinated to C228, H496, and H581, was also observed in a 3 min anaerobic soak by X-ray crystallography, whereas a 24 h soak revealed the C228-Y272 thioether bond. In solution, addition of oxygenated buffer to premat-GO preincubated with excess Cu(II) generated the Y272 radical state. On the basis of these data, a mechanism for the formation of the C228-Y272 bond and tyrosyl radical generation is proposed. The 406 nm complex is demonstrated to be a catalytically competent processing intermediate under anaerobic conditions. We propose a potential mechanism which is in common with aerobic processing by Cu(II) until the step at which the second electron acceptor is required.
Organizational Affiliation:
Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, USA.
