The precursor form ofHansenula polymorphacopper amine oxidase 1 in complex with Cu^Iand Co^II

Abstract

PDB References: apoHPAO-1, 3sx1; Co II -apoHPAO-1, 3sxx; Cu I -apoHPAO-1, 3t0u.Copper amine oxidases (CAOs) catalyze the oxidative deamination of primary amines to their corresponding aldehydes, with the concomitant reduction of O 2 to H 2 O 2 . Catalysis requires two cofactors: a mononuclear copper center and the cofactor 2,4,5-trihydroxyphenylalanine quinone (TPQ). TPQ is synthesized through the post-translational modification of an endogenous tyrosine residue and requires only oxygen and copper to proceed. TPQ biogenesis in CAO can be supported by alternate metals, albeit at decreased rates. A variety of factors are thought to contribute to the degree to which a metal can support TPQ biogenesis, including Lewis acidity, redox potential and electrostatic stabilization capability. The crystal structure has been solved of one of two characterized CAOs from the yeast Hansenula polymorpha (HPAO-1) in its metal-free (apo) form, which contains an unmodified precursor tyrosine residue instead of fully processed TPQ (HPAO-1 was denoted HPAO in the literature prior to 2010). Structures of apoHPAO-1 in complex with Cu I and Co II have also been solved, providing structural insight into metal binding prior to biogenesis.

Copper Active Sites in Biology

“…This hypothesis is supported by a crystal structure obtained for a Cu I loaded form of preprocessed HPAO, which shows a very similar site geometry to that reported by Kim et al for Cu II in preprocessed AGAO. 1230 Alternatively, the long Cu II -tyrosine distance may reflect the tyrosine remaining protonated at the pH used for crystallography (pH 6.8, pK a (Tyr) ≈ 10), resulting in a weak Cu II -tyrosine interaction rather than a Cu II -tyrosinate bond, although the presence of a bond with Cu II would be expected to drive the deprotonation of Tyr. Finally, it could be that tyrosine is not a copper ligand in anaerobic preprocessed AO and only binds to copper after O 2 is added to initiate cofactor biogenesis, a hypothesis supported by the possible assignment of the 350 nm intermediate observed by Klinman et al as a Cu II -tyrosinate species ( vide supra ).…”

The Role of Protein Crystallography in Defining the Mechanisms of Biogenesis and Catalysis in Copper Amine Oxidase

“…Structural work suggests that at this point, the tyrosine residue is present in its protonated form, as indicated by the long distance between the phenolic oxygen and bound copper in crystal structures of anaerobic Cu(I)-apoHPAO-1 and Cu(II)-apoAGAO complexes (~2.8 Å and ~2.5 Å, respectively) [69,71]. …”

“…In HPAO-1, molecular oxygen then binds in a nearby off-copper hydrophobic pocket, which induces a conformational change in the precursor tyrosine side chain such that its hydroxyl group becomes oriented toward the copper (B→C in Scheme 2 ). Structural work suggests that at this point, the tyrosine residue is present in its protonated form, as indicated by the long distance between the phenolic oxygen and bound copper in crystal structures of anaerobic Cu(I)-apoHPAO-1 and Cu(II)-apoAGAO complexes (~2.8 Å and ~2.5 Å, respectively) [ 69 , 71 ].…”

“…The crystal structures of apoHPAO-1, Cu(I)-apoHPAO-1 (prepared anaerobically) and Co(II)-apoHPAO-1 have also been reported [ 71 ]. The active sites of apoHPAO-1 and Cu(I)-apoHPAO-1 are nearly superimposable with those of apoAGAO and Cu(II)-apoAGAO, respectively [ 58 , 69 ].…”

“…The structure of Co(II)-apoHPAO-1, however, reveals that cobalt binds in apoHPAO-1 and apoAGAO with different geometries ( Figure 6 ). In apoHPAO-1, the cobalt is 5-coordinate, bound in a distorted square pyramidal geometry by the imidazole groups of three histidine residues, the precursor tyrosine residue, and an equatorial water molecule ( Figure 6A ) [ 71 ]. In contrast, cobalt in the apoAGAO structure is bound tetrahedrally by the three conserved histidine residues and the precursor tyrosine residue ( Figure 6B ) [ 77 ].…”