Polyamine oxidase

Structures of PAOs from corn, brewer's yeast, and mice contain a substrate-binding domain and an FAD-binding domain that secures the FAD cofactor non-covalently.{{Cite journal|last1=Binda|first1=Claudia|last2=Coda|first2=Alessandro|last3=Angelini|first3=Riccardo|last4=Federico|first4=Rodolfo|last5=Ascenzi|first5=Paolo|last6=Mattevi|first6=Andrea|date=1999-03-15|title=A 30 Å long U-shaped catalytic tunnel in the crystal structure of polyamine oxidase|journal=Structure|language=en|volume=7|issue=3|pages=265–276|doi=10.1016/S0969-2126(99)80037-9|pmid=10368296|issn=0969-2126|doi-access=free}}{{Cite journal|last1=Huang|first1=Qingqiu|last2=Liu|first2=Qun|last3=Hao|first3=Quan|date=2005-05-13|title=Crystal structures of Fms1 and its complex with spermine reveal substrate specificity|url=https://pubmed.ncbi.nlm.nih.gov/15843025/|journal=Journal of Molecular Biology|volume=348|issue=4|pages=951–959|doi=10.1016/j.jmb.2005.03.008|issn=0022-2836|pmid=15843025}}{{Cite journal|last1=Sjögren|first1=Tove|last2=Wassvik|first2=Carola M.|last3=Snijder|first3=Arjan|last4=Aagaard|first4=Anna|last5=Kumanomidou|first5=Taichi|last6=Barlind|first6=Louise|last7=Kaminski|first7=Tim P.|last8=Kashima|first8=Akiko|last9=Yokota|first9=Takehiro|last10=Fjellström|first10=Ola|date=2017-01-24|title=The Structure of Murine N1-Acetylspermine Oxidase Reveals Molecular Details of Vertebrate Polyamine Catabolism|url=https://doi.org/10.1021/acs.biochem.6b01140|journal=Biochemistry|volume=56|issue=3|pages=458–467|doi=10.1021/acs.biochem.6b01140|pmid=28029774|issn=0006-2960|url-access=subscription}} The active site is located at the interface of these domains.

File:Polyamine oxidase from Zea mays.png and crystallized as a dimer{{Cite journal|last=Bank|first=RCSB Protein Data|title=3D View: 1H84|journal=Covalent Adduct Between Polyamine Oxidase and N1Ethyln11((Cycloheptyl)Methyl)4,8Diazaundecane at Ph 4.6 |url=https://www.rcsb.org/3d-view/ngl/1h84|language=en}}]]

Active sites in PAOs vary, but some features are essential. The most strictly-conserved active site amino acid codons in PAO genes are a K residue at position 300 and an aromatic residue (F, Y, or H) at position 403 (numbers refer to homologous positions in the sequence of ZmPAO1, a PAO found in corn). K300 hydrogen-bonds to a water molecule, which also hydrogen-bonds to the catalytic N5 nitrogen atom of FAD. In corn, this complex modulates redox potential and reoxidation rate of the cofactor and may be involved in stabilizing the reduced cofactor or imine hydrolysis.{{Cite journal|last1=Fiorillo|first1=Annarita|last2=Federico|first2=Rodolfo|last3=Polticelli|first3=Fabio|last4=Boffi|first4=Alberto|last5=Mazzei|first5=Franco|last6=Fusco|first6=Massimo Di|last7=Ilari|first7=Andrea|last8=Tavladoraki|first8=Paraskevi|date=2011|title=The structure of maize polyamine oxidase K300M mutant in complex with the natural substrates provides a snapshot of the catalytic mechanism of polyamine oxidation|journal=The FEBS Journal|language=en|volume=278|issue=5|pages=809–821|doi=10.1111/j.1742-4658.2010.08000.x|pmid=21205212|s2cid=26000653|issn=1742-4658|doi-access=free}} The electron-dense aromatic ring at position 403 may interact with amino groups in the substrate.{{Cite journal|date=2002-07-05|title=Structure-Function Relationships in Flavoenzyme-dependent Amine Oxidations: A COMPARISON OF POLYAMINE OXIDASE AND MONOAMINE OXIDASE|journal=Journal of Biological Chemistry|language=en|volume=277|issue=27|pages=23973–23976|doi=10.1074/jbc.R200005200|pmid=12015330|issn=0021-9258|doi-access=free|last1=Binda|first1=C.|last2=Mattevi|first2=A.|last3=Edmondson|first3=D. E.}} Weak interactions with other more variable active site residues are involved in positioning the substrates.{{Cite journal|last1=Binda|first1=Claudia|last2=Angelini|first2=Riccardo|last3=Federico|first3=Rodolfo|last4=Ascenzi|first4=Paolo|last5=Mattevi|first5=Andrea|date=2001-03-01|title=Structural Bases for Inhibitor Binding and Catalysis in Polyamine Oxidase|url=https://doi.org/10.1021/bi002751j|journal=Biochemistry|volume=40|issue=9|pages=2766–2776|doi=10.1021/bi002751j|pmid=11258887|issn=0006-2960|url-access=subscription}}

In the active site, FAD oxidizes the secondary amine to an imine, which water subsequently hydrolyzes, yielding an amino-aldehyde and a primary amine. Molecular oxygen reoxidizes the FAD, generating hydrogen peroxide.

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File:PAOHYD.png{{!}}Hydride Transfer Mechanism of Polyamine Oxidation

File:PAORAD.png{{!}}Radical Mechanism of Polyamine Oxidation

File:PAONUC.png{{!}}Nucleophilic Mechanism of Polyamine Oxidation

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|caption="Three possible mechanisms of polyamine oxidation by FAD based on the structure of mouse N1-Acetylspermine Oxidase;{{Cite journal|last1=Sjögren|first1=Tove|last2=Wassvik|first2=Carola M.|last3=Snijder|first3=Arjan|last4=Aagaard|first4=Anna|last5=Kumanomidou|first5=Taichi|last6=Barlind|first6=Louise|last7=Kaminski|first7=Tim P.|last8=Kashima|first8=Akiko|last9=Yokota|first9=Takehiro|last10=Fjellström|first10=Ola|date=2017-01-24|title=The Structure of Murine N1-Acetylspermine Oxidase Reveals Molecular Details of Vertebrate Polyamine Catabolism|url=https://doi.org/10.1021/acs.biochem.6b01140|journal=Biochemistry|volume=56|issue=3|pages=458–467|doi=10.1021/acs.biochem.6b01140|pmid=28029774|issn=0006-2960|url-access=subscription}} the secondary amine oxidized must be in the charge-neutral, deprotonated state. This oxidation may proceed by hydride transfer (left), radical abstraction (center), or nucleophilic attack with a covalently-bonded cofactor-substrate intermediate (right). All three are equally plausible given the structure and none has been confirmed as the true mechanism."

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File:HYDROZXPAO.png

PAOs are central to polyamine catabolism. Different organic reaction products result in different metabolites with different fates. Because all PAO reactions release hydrogen peroxide, PAOs are tied to the metabolism of reactive oxygen species, which overlaps with pathways of programmed cell death.{{Cite journal|last1=Moschou|first1=Panagiotis N.|last2=Roubelakis-Angelakis|first2=Kalliopi A.|date=2014-03-01|title=Polyamines and programmed cell death|journal=Journal of Experimental Botany|volume=65|issue=5|pages=1285–1296|doi=10.1093/jxb/ert373|pmid=24218329|issn=0022-0957|doi-access=free}}

Polyamine catabolism is often upregulated in mammalian tumor cells. Molecules downstream of polyamine oxidation play roles in cell proliferation. Spermidine is a precursor to hypusine, which activates eukaryotic initiation factor 5A isoform 1 (eIF5A) that enables translation of mRNA. Putrescine has effects on mTOR complex 1 and eukaryotic translation initiation factor 4E (eIF4FE). Because of this, multiple anticancer drugs in various stages of clinical trial target PAOs.{{Cite journal|last1=Casero|first1=Robert A.|last2=Murray Stewart|first2=Tracy|last3=Pegg|first3=Anthony E.|date=November 2018|title=Polyamine metabolism and cancer: treatments, challenges and opportunities|journal=Nature Reviews. Cancer|volume=18|issue=11|pages=681–695|doi=10.1038/s41568-018-0050-3|issn=1474-1768|pmc=6487480|pmid=30181570}}

In plants, polyamine catabolism is tied closely to stress responses and fruit ripening.{{Cite journal|last1=Wang|first1=Wei|last2=Paschalidis|first2=Konstantinos|last3=Feng|first3=Jian-Can|last4=Song|first4=Jie|last5=Liu|first5=Ji-Hong|date=2019|title=Polyamine Catabolism in Plants: A Universal Process With Diverse Functions|journal=Frontiers in Plant Science|volume=10|pages=561|doi=10.3389/fpls.2019.00561 |pmc=6513885|pmid=31134113|issn=1664-462X|doi-access=free}}

{{CH-NH oxidoreductases}}

{{Enzymes}}

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Category:EC 1.5.3

Category:Flavoproteins

Category:Iron enzymes

Category:Enzymes of known structure