Copper cofactor biogenesis

An interesting aspect of the elucidation of the structure and mechanisms of TPQ biogenesis and function is that for these amine oxidases certain amino acid residues have multiple roles during cofactor biogenesis and catalysis. This is clearly true for the tyrosine residue, which is converted into TPQ, It has also been demonstrated by site-directed mutagenesis that a second strictly conserved tyrosine residue, which is present in the active site is also required for TPQ biogenesis and influences catalysis. Furthermore, the bound copper serves dual functions in cofactor biosynthesis, as shown in Scheme 4 as well as during catalysis. The latter function appears to be in stabilization of transient intermediates in the oxidative half reaction. ... 

Kinetic analysis of oxygen utilization during cofactor biogenesis in a copper-containing amine oxidase from yeast. Biochemistry 39, 3699-3707. 

Another aspect of considerable interest is the self-processing of TPQ, known to be derived from a protein tyrosine precursor. Copper ion is implicated in this cofactor biogenesis and the copper-dioxygen chemistry involved is discussed below. 

Over the past 10 years, our understanding of enzymes which effect the difficult chemical process of C6H bond cleavage has increased dramatically (Stubbe, 1989 Klinman, 1996). We know that nature employs both metal ions and reactive organic cofactors, such as radicals and quinones, derived by post-translational modification of aminoacids in the polypeptide chain of the enzyme. The two enzymes to be described in the present review are good examples galactose oxidase employs copper and a tyrosine covalently cross-linked to a cysteine to stabilize a radical whilst amine oxidases employ copper and tyrosine-derived quinones. There is subtle interplay between the roles played by copper in the biogenesis of these novel cofactors and in the catalytic cycle of the oxidases. 

The recent structure of the recombinant phenethylamine oxidase from Arthrobacter globiformis [30] showed the conformation for active and inactive forms of the holoenzyme and for the copper/topa quinone free apoenzyme. Basic structural parameters are in agreement with previous structural studies. The data provided further evidence for the proposed biogenesis of the cofactor and substrate entry into the active site, localizing precisely the substrate channel and its residues. A novel feature that was not described previously is the solvent filled cavity at the major interface between the two subunits of the dimer. The location of the... 

Biogenesis of the quinone cofactor of copper amine oxidases... 

Figure 7 Currently preferred mechanism for biogenesis of the topaquinone cofactor in copper-containing amine oxidase. ...

TPQ biogenesis has been proposed involving the initial formation of the [Cu(I)-Tyr] radical species and Oi binding to copper ion yielding a copper(II)-superoxide species which subsequently oxidizes the phenol of the cofactor to o-quinone. Conjugate addition of water to the o-quinone mediated by copper(II) ion forms the reduced triol form of the TPQ followed by aerobic oxidation to TPQ (Scheme 7). 

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