Copper amine oxidase: a novel use for a tyrosine

Copper homeostasis and copper-induced cell death： Novel targeting for intervention in the pathogenesis of vascular aging

Copper-induced cell death, also known as cuproptosis, is distinct from other types of cell death such as apoptosis, necrosis, and ferroptosis. It can trigger the accumulation of lethal reactive oxygen species, leading to the onset and progression of aging. The significant increases in copper ion levels in the aging populations confirm a close relationship between copper homeostasis and vascular aging. On the other hand, vascular aging is also closely related to the occurrence of various cardiovascular diseases throughout the aging process. However, the specific causes of vascular aging are not clear, and different living environments and stress patterns can lead to individualized vascular aging. By exploring the correlations between copper-induced cell death and vascular aging, we can gain a novel perspective on the pathogenesis of vascular aging and enhance the prognosis of atherosclerosis. This article aims to provide a comprehensive review of the impacts of copper homeostasis on vascular aging, including their effects on endothelial cells, smooth muscle cells, oxidative stress, ferroptosis, intestinal flora, and other related factors. Furthermore, we intend to discuss potential strategies involving cuproptosis and provide new insights for copper-related vascular aging.

Molecular cloning, expression, and functional analysis of the copper amine oxidase gene in the endophytic fungus Shiraia sp. Slf14 from Huperzia serrata

Huperzine A (HupA) is a drug used for the treatment of Alzheimer's disease. However, the biosynthesis of this medicinally important compound is not well understood. The HupA biosynthetic pathway is thought to be initiated by the decarboxylation of lysine to form cadaverine, which is then converted to 5-aminopentanal by copper amine oxidase (CAO). In this study, we cloned and expressed an SsCAO gene from a HupA-producing endophytic fungus, Shiraia sp. Slf14. Analysis of the deduced protein amino acid sequence showed that it contained the Asp catalytic base, conserved motif Asn-Tyr-Asp/Glu, and three copper-binding histidines. The cDNA of SsCAO was amplified and expressed in Escherichia coli BL21(DE3), from which a 76 kDa protein was obtained. The activity of this enzyme was tested, which provided more information about the SsCAO gene in the endophytic fungus. Gas Chromatograph-Mass Spectrometry (GC-MS) revealed that this SsCAO could accept cadaverine as a substrate to produce 5-aminopentanal, the precursor of HupA. Phylogenetic tree analysis indicated that the SsCAO from Shiraia sp. Slf14 was closely related to Stemphylium lycopersici CAO. This is the first report on the cloning and expression of a CAO gene from HupA-producing endophytic fungi. Functional characterization of this enzyme provides new insights into the biosynthesis of the HupA an anti-Alzheimer's drug.

The other Topa: formation of 3,4,5-trihydroxyphenylalanine in peptides

Hydroxylation of peptidyl-3,4-dihydroxyphenyl-l-alanine (Dopa) was observed during tyrosinase incubation of a decapeptide related to the mussel adhesive protein mefp1. The reaction was carried out at high enzyme concentrations (700 units tyrosinase/micromol of tyrosine). The hydroxylation of tyrosines in the decapeptide proceeds sequentially. First, Tyr-9 is hydroxylated to Dopa, followed by hydroxylation of Tyr-5; finally, Dopa-9 is hydroxylated to Topa. Topa was identified as 3,4,5-trihydroxyphenylalanine (3,4,5-Topa) by comparison to known standards using amino acid analysis, derivatization with phenylisothiocyanate in combination with Edman sequencing, and matrix-assisted laser desorption mass spectrometry with time-of-flight. Two other peptides, not related to mussel proteins, were also found to form peptidyl-Topa upon incubation with tyrosinase. Although 3,4,5-Topa has been reported in the primary sequence of several peptides, its formation in vitro from tyrosine-containing peptides is novel. The formation of Topa would appear to be a function of tyrosinase rather than the nucleophilic addition of water to dopaquinone.

Agmatine oxidation by copper amine oxidase

The product of agmatine oxidation catalyzed by Pisum sativum L. copper amine oxidase has been identified by means of one- and two-dimensional (1)H-NMR spectroscopy to be N-amidino-2-hydroxypyrrolidine. This compound inhibits competitively rat nitric oxide synthase type I and type II (NOS-I and NOS-II, respectively) and bovine trypsin (trypsin) activity, values of Ki being (1.1 +/- 0.1) x 10(-5) m (at pH 7.5 and 37.0 degrees C), (2.1 +/- 0.1) x 10(-5) m (at pH 7.5 and 37.0 degrees C), and (8.9 +/- 0.4) x 10(-5) m (at pH 6.8 and 21.0 degrees C), respectively. Remarkably, the affinity of N-amidino-2-hydroxypyrrolidine for NOS-I, NOS-II and trypsin is significantly higher than that observed for agmatine and clonidine binding. Furthermore, N-amidino-2-hydroxypyrrolidine and agmatine are more efficient than clonidine in displacing [(3)H]clonidine (= 1.0 x 10(-8) m) from specific binding sites in heart rat membranes, values of IC50 being (1.3 +/- 0.4) x 10(-9) m and (2.2 +/- 0.4) x 10(-8) m, respectively (at pH 7.4 and 37.0 degrees C).

A study on the reactions of plant copper amine oxidase with C3 and C4 aliphatic diamines

The paper reports a study on the reactions of grass pea (Lathyrus sativus) amine oxidase (GPAO) with several aliphatic diamines. The influence of the chain length and of unsaturations in the molecules was examined. Kinetic measurements confirmed that trans-, i.e., (E)-2-butene-1,4-diamine (TDABE) and cis-, i.e., (Z)-2-butene-1,4-diamine (CDABE) could be classified as good substrates. Propane-1,3-diamine (DAP) and propene-1,3-diamine (DAPE) were only weakly oxidized, whereas 1,3-diamino-2-propanol (DAPL) was not utilized as a substrate. Contrary to the inactivator 2-butyne-1,4-diamine (DABI), DAPE was shown to be only a competitive inhibitor. DAP itself did not inhibit the catalytic activity. Irreversible inhibition of the activity occurred only after the incubation of GPAO with DABI; other diamines were without this effect. Differential pulse polarography and chromatofocusing confirmed that the aminoaldehyde product of DABI oxidation binds to the enzyme. Activity assay of pea aminoaldehyde dehydrogenase enabled us to detect the products of the oxidation of TDABE, CDABE, and DAP by GPAO. As the product of DAP oxidation, 3-amino-propanal (APAL) was detected by mass spectrometry and confirmed to be a potent noncompetitive inhibitor of GPAO. The absorption changes that occurred in the course of the reaction of GPAO with the diamines were investigated using rapid-scanning spectrophotometry. DABI, TDABE, CDABE, DAP, and DAPE reacted with GPAO providing characteristic maxima of the Cu(I)-semiquinolamine species that is formed in the catalytic cycle. The results presented here confirm that with the exception of DAPL, all the studied diamines could be classified as GPAO substrates, but only DABI can be considered as a mechanism-based inhibitor.

Cloning and Characterization of Mouse Vascular Adhesion Protein-1 Reveals a Novel Molecule with Enzymatic Activity

Human vascular adhesion protein-1 (VAP-1) is a sialylated endothelial cell adhesion molecule mediating the initial L-selectin-independent interactions between lymphocytes and endothelial cells in man. In this work we cloned and characterized mouse VAP-1 (mVAP-1) and produced an anti-mVAP-1 mAb against a recombinant mVAP-1 fusion protein. The isolated cDNA encodes a novel 84.5-kDa mouse molecule. The anti-mVAP-1 mAb stained high endothelial venules in peripheral lymph nodes, and smooth muscle cells and lamina propria vessels in gut. During immunoblotting, this anti-mVAP-1 mAb recognized a 110/220-kDa Ag, suggesting that mVAP-1 is a dimer. Since mVAP-1 has significant sequence identity to members of a family of enzymes called the copper-containing amine oxidases, we showed that mVAP-1 possesses monoamine oxidase activity. Thus, mVAP-1 is the first mouse membrane-bound amine oxidase identified at the molecular level. Based on the 83% identity between the isolated cDNA and human VAP-1 cDNA, the expression pattern, the molecular mass, and the enzyme activity against monoamines, the cloned molecule represents a mouse homologue of human VAP-1. Cloning of mVAP-1 provides a valuable tool for in vivo studies of the significance of VAP-1 for lymphocyte-endothelial cell interactions and of the possible relationship between leukocyte adhesion and amine oxidase activity.

Effect of metal on 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis in the Hansenula polymorpha copper amine oxidase

Previous studies of wild-type and mutant forms of a recombinant copper amine oxidase from Hansenula polymorpha, expressed in Saccharomyces cerevisiae, have indicated a self-processing mechanism for 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis involving the active site copper (Cai, D., and Klinman, J. P. (1994) J. Biol. Chem. 269, 32039-32042). In contrast to prokaryotic copper amine oxidases, however, it has not been possible to initiate topa quinone formation by the addition of exogenous copper to precursor H. polymorpha amine oxidase lacking copper. Metal analysis of copper-depleted wild-type enzyme reveals 0.2-0.3 mol copper, together with 0.6 mol zinc. Despite changes in the zinc and copper levels in growth media, the level of zinc in purified enzyme remains fairly constant. Further, we have been unable to displace protein-bound zinc by exogenously added copper. The H. polymorpha amine oxidase gene was subsequently expressed in Escherichia coli and found to be almost completely free of copper and zinc. In vitro reconstitution of this apoprotein confirms that zinc binds to H. polymorpha amine oxidase and prevents reconstitution with copper. By contrast, addition of copper first to apoprotein leads to formation of topa quinone and stable activity in the presence of added zinc. These findings indicate efficient binding of either zinc or copper to a site that undergoes little or no exchange. The data confirm that topa quinone biogenesis in the H. polymorpha system is catalyzed by copper and occurs in the absence of added factors. We conclude that the mechanisms of cofactor biogenesis in pro- and eukaryotic systems are likely to be similar or identical. The results described herein imply different pathways for the in vivo assembly of heterologously expressed amine oxidases in S. cerevisiae and E. coli.

Novel metal sites in protein structures

Recently, the three-dimensional structures of several novel metalloenzymes have been solved. Of special interest are those containing uncommon and/or not well characterized metals such as molybdenum, tungsten, nickel, vanadium and cobalt. Modulated by the protein environment, the specific properties of these metals and of special metal-binding cofactors such as siroheme and topa quinone are used to catalyze a vast array of fascinating reactions.

Crystal structure of a eukaryotic (pea seedling) copper-containing amine oxidase at 2.2 A resolution

BACKGROUND

Copper-containing amine oxidases catalyze the oxidative deamination of primary amines to aldehydes, in a reaction that requires free radicals. These enzymes are important in many biological processes, including cell differentiation and growth, would healing, detoxification and signalling. The catalytic reaction requires a redox cofactor, topa quinone (TPQ), which is derived by post-translational modification of an invariant tyrosine residue. Both the biogenesis of the TPQ cofactor and the reaction catalyzed by the enzyme require the presence of a copper atom at the active site. The crystal structure of a prokaryotic copper amine oxidase from E. coli (ECAO) has recently been reported.

RESULTS

The first structure of a eukaryotic (pea seedling) amine oxidase (PSAO) has been solved and refined at 2.2 A resolution. The crystallographic phases were derived from a single phosphotungstic acid derivative. The positions of the tungsten atoms in the W12 clusters were obtained by molecular replacement using E. coli amine oxidase as a search model. The methodology avoided bias from the search model, and provides an essentially independent view of a eukaryotic amine oxidase. The PSAO molecule is a homodimer; each subunit has three domains. The active site of each subunit lies near an edge of the beta-sandwich of the largest domain, but is not accessible from the solvent. The essential active-site copper atom is coordinated by three histidine side chains and two water molecules in an approximately square-pyramidal arrangement. All the atoms of the TPQ cofactor are unambiguously defined, the shortest distance to the copper atom being approximately 6 A.

CONCLUSIONS

There is considerable structural homology between PSAO and ECAO. A combination of evidence from both structures indicates that the TPQ side chain is sufficiently flexible to permit the aromatic grouf to rotate about the Cbeta-Cgamma bond, and to move between bonding and non-bonding positions with respect to the Cu atom. Conformational flexibility is also required at the surface of the molecule to allow the substrates access to the active site, which is inaccessible to solvent, as expected for an enzyme that uses radical chemistry.