Trapping of a dopaquinone intermediate in the TPQ cofactor biogenesis in a copper-containing amine oxidase from Arthrobacter globiformis

Insight into the Spatial Arrangement of the Lysine Tyrosylquinone and Cu2+ in the Active Site of Lysyl Oxidase-like 2

Lysyl oxidase-2 (LOXL2) is a Cu²⁺ and lysine tyrosylquinone (LTQ)-dependent amine oxidase that catalyzes the oxidative deamination of peptidyl lysine and hydroxylysine residues to promote crosslinking of extracellular matrix proteins. LTQ is post-translationally derived from Lys653 and Tyr689, but its biogenesis mechanism remains still elusive. A 2.4 Å Zn²⁺-bound precursor structure lacking LTQ (PDB:5ZE3) has become available, where Lys653 and Tyr689 are 16.6 Å apart, thus a substantial conformational rearrangement is expected to take place for LTQ biogenesis. However, we have recently shown that the overall structures of the precursor (no LTQ) and the mature (LTQ-containing) LOXL2s are very similar and disulfide bonds are conserved. In this study, we aim to gain insights into the spatial arrangement of LTQ and the active site Cu²⁺ in the mature LOXL2 using a recombinant LOXL2 that is inhibited by 2-hydrazinopyridine (2HP). Comparative UV-vis and resonance Raman spectroscopic studies of the 2HP-inhibited LOXL2 and the corresponding model compounds and an EPR study of the latter support that 2HP-modified LTQ serves as a tridentate ligand to the active site Cu². We propose that LTQ resides within 2.9 Å of the active site of Cu²⁺ in the mature LOXL2, and both LTQ and Cu²⁺ are solvent-exposed.

Mass Spectrometry-Based Disulfide Mapping of Lysyl Oxidase-like 2

Lysyl oxidase-like 2 (LOXL2) catalyzes the oxidative deamination of peptidyl lysines and hydroxylysines to promote extracellular matrix remodeling. Aberrant activity of LOXL2 has been associated with organ fibrosis and tumor metastasis. The lysine tyrosylquinone (LTQ) cofactor is derived from Lys653 and Tyr689 in the amine oxidase domain via post-translational modification. Based on the similarity in hydrodynamic radius and radius of gyration, we recently proposed that the overall structures of the mature LOXL2 (containing LTQ) and the precursor LOXL2 (no LTQ) are very similar. In this study, we conducted a mass spectrometry-based disulfide mapping analysis of recombinant LOXL2 in three forms: a full-length LOXL2 (fl-LOXL2) containing a nearly stoichiometric amount of LTQ, Δ1-2SRCR-LOXL2 (SRCR1 and SRCR2 are truncated) in the precursor form, and Δ1-3SRCR-LOXL2 (SRCR1, SRCR2, SRCR3 are truncated) in a mixture of the precursor and the mature forms. We detected a set of five disulfide bonds that is conserved in both the precursor and the mature recombinant LOXL2s. In addition, we detected a set of four alternative disulfide bonds in low abundance that is not associated with the mature LOXL2. These results suggest that the major set of five disulfide bonds is retained post-LTQ formation.

Molecular mechanism of a large conformational change of the quinone cofactor in the semiquinone intermediate of bacterial copper amine oxidase

Copper amine oxidase from Arthrobacter globiformis (AGAO) catalyses the oxidative deamination of primary amines via a large conformational change of a topaquinone (TPQ) cofactor during the semiquinone formation step. This conformational change of TPQ occurs in the presence of strong hydrogen bonds and neighboring bulky amino acids, especially the conserved Asn381, which restricts TPQ conformational changes over the catalytic cycle. Whether such a semiquinone intermediate is catalytically active or inert has been a matter of debate in copper amine oxidases. Here, we show that the reaction rate of the Asn381Ala mutant decreases 160-fold, and the X-ray crystal structures of the mutant reveals a TPQ-flipped conformation in both the oxidized and reduced states, preceding semiquinone formation. Our hybrid quantum mechanics/molecular mechanics (QM/MM) simulations show that the TPQ conformational change is realized through the sequential steps of the TPQ ring-rotation and slide. We determine that the bulky side chain of Asn381 hinders the undesired TPQ ring-rotation in the oxidized form, favoring the TPQ ring-rotation in reduced TPQ by a further stabilization leading to the TPQ semiquinone form. The acquired conformational flexibility of TPQ semiquinone promotes a high reactivity of Cu(i) to O₂, suggesting that the semiquinone form is catalytically active for the subsequent oxidative half-reaction in AGAO. The ingenious molecular mechanism exerted by TPQ to achieve the “state-specific” reaction sheds new light on a drastic environmental transformation around the catalytic center.

The large conformational change of topaquinone in bacterial copper amine oxidase occurs through the TPQ ring rotation and slide, which are essential to stabilize the semiquinone form.

Formation of Ni(II)-phenoxyl radical complexes by O2: a mechanistic insight into the reaction of Ni(II)-phenol complexes with O2

A reaction of Ni(ClO4)2·6H2O with a tripodal ligand having two di(tert-butyl)phenol moieties, H2tbuL, and 1 equivalent of triethylamine in CH2Cl2/CH3OH (1 : 1, v/v) under N2 gave a NiII-(phenol)(phenolate) complex, [Ni(HtbuL)(CH3OH)2]ClO4. The formation of the NiII-phenoxyl radical complex by O2 was observed in the reaction of this complex in the solid state. On the other hand, the NiII-phenoxyl radical complex [Ni(Me2NL)(CH3OH)2]ClO4 was obtained by the reaction of H2Me2NL having a p-(dimethylamino)phenol moiety with Ni(ClO4)2·6H2O in a similar procedure under O2, through the oxidation of the NiII-(phenol)(phenolate) complex. However, a direct redox reaction of the NiII ion could not be detected in the phenoxyl radical formation. The results of the reaction kinetics, XAS and X-ray structure analyses suggested that the O2 oxidation from the NiII-(phenol)(phenolate) complex to the NiII-phenoxyl radical complex occurs via the proton transfer-electron transfer (PT-ET) type mechanism of the phenol moiety weakly coordinated to the nickel ion.

Reaction mechanism of lysyl oxidase-like 2 (LOXL2) studied by computational methods

Lysyl oxidase-like 2 (LOXL2) is a copper-dependent amine oxidase that catalyzes the oxidative deamination of the ε-amino group of lysines/hydroxylysines on substrate proteins (collagen and elastin) to form aldehyde groups. The generated aldehyde groups are of significance in crosslinking with the adjacent aldehyde or ε-amino group on proteins in extracellular matrix. In this paper, we have studied the reaction mechanism of LOXL2 by means of quantum mechanics (QM) and combined QM and molecular mechanics (QM/MM) methods. This study is divided into two parts, i.e. the biosynthesis of lysine tyrosylquinone (LTQ) cofactor and oxidative deamination of ε-amino group of lysine by LTQ. For the former part, the reaction is driven by a large exothermicity of about 284 kJ/mol. Dopaquinone radical (DPQr) is suggested to be an intermediate state in this reaction. In addition, His652 residue is predicted to serve as proton acceptor. The rate-determining step for the biosynthesis of LTQ is found to be hydrogen-atom abstraction from the benzene ring on substrate by Cu²⁺-hydroxide, which is a proton-coupled electron transfer (PCET) process with an energy barrier of 84 kJ/mol. For the latter part, the reaction is exothermic by about 145 kJ/mol, and the copper ion is proposed to play a role of redox catalyst in the last step to generate the product of aldehyde. However, the copper ion might not be indispensable for the latter part, which is consistent with the previous study.

Formation of the CuII -Phenoxyl Radical by Reaction of O2 with a CuII -Phenolate Complex via the CuI -Phenoxyl Radical

Reaction of Cu(ClO₄ )₂ ⋅6 H₂ O with a tripodal 2N2O ligand, H₂ Me₂ NL, having a p-(dimethylamino)phenol moiety, in CH₂ Cl₂ /MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me₂ NL)(H₂ O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me₂ NL)(MeOH)]ClO₄ (2), which could be obtained also from the isolated complex 1 by reaction with O₂ in CH₂ Cl₂ /MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic Cu^II EPR signals of the d x 2 - y 2 ground state in CH₂ Cl₂ /MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the Cu^II -(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH₂ Cl₂ solution of 1 exhibits distortion from the d x 2 - y 2 ground state and a temperature-dependent equilibrium between the Cu^II -(dimethylamino)phenolate and the Cu^I -(dimethylamino)phenoxyl radical. From these results, Cu^II -phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O₂ via the Cu^I -phenoxyl radical species.

Characterization of PlGoxB, a flavoprotein required for cysteine tryptophylquinone biosynthesis in glycine oxidase from Pseudoalteromonas luteoviolacea

LodA-like proteins are oxidases with a protein-derived cysteine tryptophylquinone (CTQ) prosthetic group. In Pseudoalteromonas luteoviolacea glycine oxidase (PlGoxA), CTQ biosynthesis requires post-translational modifications catalyzed by a modifying enzyme encoded by PlgoxB. The PlGoxB protein was expressed and shown to possess a flavin cofactor. PlGoxB was unstable in solution as it readily lost the flavin and precipitated. PlGoxB precipitation was significantly reduced by incubation with either excess FAD or an equal concentration of prePlGoxA, the precursor protein that is its substrate. In contrast, the mature CTQ-bearing PlGoxA had no stabilizing effect. A homology model of PlGoxB was generated using the structure of Alkylhalidase CmIS. The FAD-binding site of PlGoxB in the model was nearly identical to that of the template structure. The bound FAD in PlGoxB had significant solvent exposure, consistent with the observed tendency to lose FAD. This also suggested that interaction of prePlGoxA with PlGoxB at the exposed FAD-binding site could prevent the observed loss of FAD and subsequent precipitation of PlGoxB. A docking model of the putative PlGoxB-prePlGoxA complex was consistent with these hypotheses. The experimental results and computational analysis implicate structural features of PlGoxB that contribute to its stability and function.

A Three-Dimensional Model of Human Lysyl Oxidase, a Cross-Linking Enzyme

Lysyl oxidase (LOX) is a cross-linking enzyme identified 50 years ago, but its 3D structure is still unknown. We have thus built a 3D model of human LOX by homology modeling using the X-ray structure of human lysyl oxidase-like 2 as a template. This model is the first one to recapitulate all known biochemical features of LOX, namely, the coordination of the copper ion and the formation of the lysine tyrosylquinone cofactor and the disulfide bridges. Furthermore, this model is stable during a 1 μs molecular dynamics simulation. The catalytic site is located in a groove surrounded by two loops. The distance between these loops fluctuated during the simulations, which suggests that the groove forms a hinge with a variable opening, which is able to accommodate the various sizes of LOX substrates. This 3D model is a pre-requisite to perform docking experiments with LOX substrates and other partners to identify binding sites and to design new LOX inhibitors specific for therapeutic purpose.

Diversity of structures, catalytic mechanisms and processes of cofactor biosynthesis of tryptophylquinone-bearing enzymes

Tryptophyquinone-bearing enzymes contain protein-derived cofactors formed by posttranslational modifications of Trp residues. Tryptophan tryptophylquinone (TTQ) is comprised of a di-oxygenated Trp residue, which is cross-linked to another Trp residue. Cysteine tryptophylquinone (CTQ) is comprised of a di-oxygenated Trp residue, which is cross-linked to a Cys residue. Despite the similarity of these cofactors, it has become evident in recent years that the overall structures of the enzymes that possess these cofactors vary, and that the gene clusters that encode the enzymes are quite diverse. While it had been long assumed that all tryptophylquinone enzymes were dehydrogenases, recently discovered classes of these enzymes are oxidases. A common feature of enzymes that have these cofactors is that the posttranslational modifications that form the mature cofactors are catalyzed by a modifying enzyme. However, it is now clear that modifying enzymes are different for different tryptophylquinone enzymes. For methylamine dehydrogenase a di-heme enzyme, MauG, is needed to catalyze TTQ biosynthesis. However, no gene similar to mauG is present in the gene clusters that encode the other enzymes, and the recently characterized family of CTQ-dependent oxidases, termed LodA-like proteins, require a flavoenzyme for cofactor biosynthesis.

Conformational Design and Characterisation of a Truncated Diamine Oxidase from Arthrobacter globiformis

A functional mini protein can be developed by miniaturising its size. The minimisation technique provides an excellent model system for studying native enzymes, especially in creating an alternative novel biocatalyst. Miniaturised proteins may have enhanced stability, a crucial characteristic for large-scale production and industrial applications. In this study, a huge enzyme molecule, known as diamine oxidase (DAO, comprising 700 amino acids), was selected to undergo the process. By retaining the arrangement of the original functional sites of DAO in the fourth domain, a mini DAO can be designed via homology modelling. After several downsizing processes, a final configuration of 220 amino acids displayed high binding affinity towards histamine, a short-chain substrate that was catalysed by the parental DAO. The configuration also showed enhanced affinity towards a long-chain substrate known as spermidine. The gene for the designed protein was cloned and expressed in pET102/TOPO vector and overexpressed in E. coli BL21 (DE3). The new mini DAO had similar temperature tolerance and versatile substrates specificity characteristics as its parental protein. An active mini-protein with these characteristics is potentially useful for several applications such as detecting biogenic amines in the biological fluids and the environment that may give rise to health issues.

Protein-Derived Cofactors Revisited: Empowering Amino Acid Residues with New Functions

A protein-derived cofactor is a catalytic or redox-active site in a protein that is formed by post-translational modification of one or more amino acid residues. These post-translational modifications are irreversible and endow the modified amino acid residues with new functional properties. This Perspective focuses on the following advances in this area that have occurred during recent years. The biosynthesis of the tryptophan tryptophylquinone cofactor is catalyzed by a diheme enzyme, MauG. A bis-Fe^IV redox state of the hemes performs three two-electron oxidations of specific Trp residues via long-range electron transfer. In contrast, a flavoenzyme catalyzes the biosynthesis of the cysteine tryptophylquinone (CTQ) cofactor present in a newly discovered family of CTQ-dependent oxidases. Another carbonyl cofactor, the pyruvoyl cofactor found in classes of decarboxylases and reductases, is formed during an apparently autocatalytic cleavage of a precursor protein at the N-terminus of the cleavage product. It has been shown that in at least some cases, the cleavage is facilitated by binding to an accessory protein. Tyrosylquinonine cofactors, topaquinone and lysine tyrosylquinone, are found in copper-containing amine oxidases and lysyl oxidases, respectively. The physiological roles of different families of these enzymes in humans have been more clearly defined and shown to have significant implications with respect to human health. There has also been continued characterization of the roles of covalently cross-linked amino acid side chains that influence the reactivity of redox-active metal centers in proteins. These include Cys-Tyr species in galactose oxidase and cysteine dioxygenase and the Met-Tyr-Trp species in the catalase-peroxidase KatG.

Protein oxidation involved in Cys-Tyr post-translational modification

Some post-translationally modified tyrosines can perform reversible redox chemistry similar to metal cofactors. The most studied of these tyrosine modifications is the intramolecular thioether-crosslinked 3'-(S-cysteinyl)-tyrosine (Cys-Tyr) in galactose oxidase. This Cu-mediated tyrosine modification in galactose oxidase involves direct electron transfer (inner-sphere) to the coordinated tyrosine. Mammalian cysteine dioxygenase enzymes also contain a Cys-Tyr that is formed, presumably, through outer-sphere electron transfer from a non-heme iron center ~6Å away from the parent residues. An orphan protein (BF4112), amenable to UV spectroscopic characterization, has also been shown to form Cys-Tyr between Tyr 52 and Cys 98 by an adjacent Cu²⁺ ion-loaded, mononuclear metal ion binding site. Native Cys-Tyr fluorescence under denaturing conditions provides a more robust methodology for Cys-Tyr yield determination. Cys-Tyr specificity, relative to 3,3'-dityrosine, was provided in this fluorescence assay by guanidinium chloride. Replacing Tyr 52 with Phe or the Cu²⁺ ion with a Zn²⁺ ion abolished Cys-Tyr formation. The Cys-Tyr fluorescence-based yields were decreased but not completely removed by surface Tyr mutations to Phe (Y4F/Y109F, 50%) and Cys 98 to Ser (25%). The small absorbance and fluorescence emission intensities for C98S BF4112 were surprising until a significantly red-shifted emission was observed. The red-shifted emission spectrum and monomer to dimer shift seen by reducing, denaturing SDS-PAGE demonstrate a surface tyrosyl radical product (dityrosine) when Cys 98 is replaced with Ser. These results demonstrate surface tyrosine oxidation in BF4112 during Cys-Tyr formation and that protein oxidation can be a significant side reaction in forming protein derived cofactors.

Activation of dioxygen by copper metalloproteins and insights from model complexes

Nature uses dioxygen as a key oxidant in the transformation of biomolecules. Among the enzymes that are utilized for these reactions are copper-containing metalloenzymes, which are responsible for important biological functions such as the regulation of neurotransmitters, dioxygen transport, and cellular respiration. Enzymatic and model system studies work in tandem in order to gain an understanding of the fundamental reductive activation of dioxygen by copper complexes. This review covers the most recent advancements in the structures, spectroscopy, and reaction mechanisms for dioxygen-activating copper proteins and relevant synthetic models thereof. An emphasis has also been placed on cofactor biogenesis, a fundamentally important process whereby biomolecules are post-translationally modified by the pro-enzyme active site to generate cofactors which are essential for the catalytic enzymatic reaction. Significant questions remaining in copper-ion-mediated O2-activation in copper proteins are addressed.

Roles of Copper and a Conserved Aspartic Acid in the Autocatalytic Hydroxylation of a Specific Tryptophan Residue during Cysteine Tryptophylquinone Biogenesis

The first posttranslational modification step in the biosynthesis of the tryptophan-derived quinone cofactors is the autocatalytic hydroxylation of a specific Trp residue at position C-7 on the indole side chain. Subsequent modifications are catalyzed by modifying enzymes, but the mechanism by which this first step occurs is unknown. LodA possesses a cysteine tryptophylquinone (CTQ) cofactor. Metal analysis as well as spectroscopic and kinetic studies of the mature and precursor forms of a D512A LodA variant provides evidence that copper is required for the initial hydroxylation of the precursor protein and that if alternative metals are bound, the modification does not occur and the precursor is unstable. It is shown that the mature native LodA also contains loosely bound copper, which affects the visible absorbance spectrum and quenches the fluorescence spectrum that is attributed to the mature CTQ cofactor. When copper is removed, the fluorescence appears, and when it is added back to the protein, the fluorescence is quenched, indicating that copper reversibly binds in the proximity of CTQ. Removal of copper does not diminish the enzymatic activity of LodA. This distinguishes LodA from enzymes with protein-derived tyrosylquinone cofactors in which copper is present near the cofactor and is absolutely required for activity. Mechanisms are proposed for the role of copper in the hydroxylation of the unactivated Trp side chain. These results demonstrate that the reason that the highly conserved Asp512 is critical for LodA, and possibly all tryptophylquinone enzymes, is not because it is required for catalysis but because it is necessary for CTQ biosynthesis, more specifically to facilitate the initial copper-dependent hydroxylation of a specific Trp residue.

Cu(II)-mediated phenol oxygenation: chemical evidence implicates a unique role of the enzyme active site in promoting the chemically difficult tyrosine monooxygenation in TPQ cofactor biogenesis of copper amine oxidases

Cu(II)-mediated autoxidations of 4-tert-butylphenol under various conditions was studied, the data confirmed imidazole is the best ligand to promote phenol oxygenation. The same reaction of 2,4-di-tert-butylphenol proceeded much more quickly to lead nearly exclusively to oxidative coupling rather than oxygenation under high pressure O2. These results suggested that Cu(II)-catalyzed phenol autoxidation by activating O2 and phenol in terms of a phenoxy radical (ArO)-Cu(II)-superoxide ternary complex, whereas selectivity between oxygenation and coupling depends mainly on the electronic structure of ArO. It is appeared that CuAOs could achieve stoichiometric tyrosine monooxygenation by modulating the redox potential of Cu(II) and stabilizing the ternary complex through protein conformational adjustment.

Human lysyl oxidase-like 2

Lysyl oxidase like-2 (LOXL2) belongs to the lysyl oxidase (LOX) family, which comprises Cu(2+)- and lysine tyrosylquinone (LTQ)-dependent amine oxidases. LOXL2 is proposed to function similarly to LOX in the extracellular matrix (ECM) by promoting crosslinking of collagen and elastin. LOXL2 has also been proposed to regulate extracellular and intracellular cell signaling pathways. Dysregulation of LOXL2 has been linked to many diseases, including cancer, pro-oncogenic angiogenesis, fibrosis and heart diseases. In this review, we will give an overview of the current understandings and hypotheses regarding the molecular functions of LOXL2.

Human copper-dependent amine oxidases

Copper amine oxidases (CAOs) are a class of enzymes that contain Cu(2+) and a tyrosine-derived quinone cofactor, catalyze the conversion of a primary amine functional group to an aldehyde, and generate hydrogen peroxide and ammonia as byproducts. These enzymes can be classified into two non-homologous families: 2,4,5-trihydroxyphenylalanine quinone (TPQ)-dependent CAOs and the lysine tyrosylquinone (LTQ)-dependent lysyl oxidase (LOX) family of proteins. In this review, we will focus on recent developments in the field of research concerning human CAOs and the LOX family of proteins. The aberrant expression of these enzymes is linked to inflammation, fibrosis, tumor metastasis/invasion and other diseases. Consequently, there is a critical need to understand the functions of these proteins at the molecular level, so that strategies targeting these enzymes can be developed to combat human diseases.

MCF-7 cells expressing nuclear associated lysyl oxidase-like 2 (LOXL2) exhibit an epithelial-to-mesenchymal transition (EMT) phenotype and are highly invasive in vitro

LOXL2 is a copper- and lysine tyrosylquinone-dependent amine oxidase that has been proposed to function both extracellularly and intracellularly to activate oncogenic signaling pathways leading to EMT and invasion of breast cancer cells. In this study, we selected MCF-7 cells that stably express forms of recombinant LOXL2 differing in their subcellular localizations and catalytic competencies. This enabled us to dissect the molecular functions of intracellular and extracellular LOXL2s and examine their contributions to breast cancer metastasis/invasion. We discovered that secreted LOXL2 (~100-kDa) is N-glycosylated at Asn-455 and Asn-644, whereas intracellular LOXL2 (~75-kDa) is nonglycosylated and N-terminally processed, and is primarily associated with the nucleus. Both forms of LOXL2 can oxidize lysine in solution. However, we found that expression of intracellular LOXL2 is more strongly associated with EMT and invasiveness than secreted LOXL2 in vitro. The results indicate that nuclear associated LOXL2 contributes to the stabilization of Snail1 transcription factor at the protein level to induce EMT and promote invasion in vitro, through repression of E-cadherin, occludin, and estrogen receptor-α, and up-regulation of vimentin, fibronectin, and MT1-MMP.

Lysyl oxidase genetic variants and the prognosis of glioma

Lysyl oxidase (LOX) is a copper-dependent amine oxidase that plays important roles in the development and homeostasis of primary brain tumors such as glioma. The aim of this study was to investigate whether polymorphisms in the LOX gene were associated with susceptibility to glioma. We tested two functional polymorphisms of LOX, -22G/C and 473G/A, and compared them between 466 glioma cases and 502 healthy controls in the Chinese population. Results showed that the prevalence of 473AA genotype was significantly increased in cases than in controls (p = 0.001). Individuals who carried 473A allele had a 1.44-fold of increased risk for glioma than those with 473G allele (p = 0.002). In addition, when analyzing the survival time of glioma patients with LOX 473G/A polymorphism, cases with AA genotype had significantly shorter survival time compared to the patients carrying G allele (25.0 months vs 43.0 months, p = 0.0009). These results suggested that polymorphism in LOX gene was associated with increased susceptibility to glioma and could be used as prognostic factor for this malignancy.

The effect of lysyl oxidase polymorphism on susceptibility and prognosis of nonsmall cell lung cancer

Lysyl oxidase (LOX) is a copper-dependent amine oxidase that plays important roles in development and homeostasis of the lungs. The aim of this study was to investigate whether polymorphisms in the LOX gene were associated with susceptibility to nonsmall cell lung cancer (NSCLC). We sequenced the promoter region of LOX gene and tested the previously reported polymorphism 473 G/A in the Han Chinese population. A novel polymorphism, -22 G/C, was identified in the promoter region of LOX. However, it did not show any correlation with NSCLC. Frequencies of the 473AA genotype and 473A allele were significantly higher in the NSCLC cases than in control group (p = 0.004 and p = 0.006, respectively). Further, our results showed that survival time of NSCLC patients with 473AA genotype was significantly shorter compared to the cases carrying 473 G allele (20.0 months vs. 28.0 months, p = 0.011). These data indicate that LOX 473 G/A polymorphism is associated with increased risk of NSCLC and can be a prognostic predictor for this disease.

One-copper laccase-related enzyme from Marasmius sp.: purification, characterization and bleaching of textile dyes

In the culture filtrate of a Marasmius sp. strain isolated in Indonesia during a screening for fungi with the ability to decolorize textile dyes, two laccase-related enzymes (laccase-related enzyme I and II) were detected. Laccase-related enzyme I was purified to homogeneity by ion exchange and hydrophobic interaction chromatography. The native enzyme was shown to have a molecular mass of 53 kDa, an N-terminal amino acid sequence characteristically seen in laccases and an isoelectric point of pH 3.8. The enzyme accepts typical laccase substrates including 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), syringaldazine and guaiacol, but has no tyrosinase activity. The pH optimum is at pH 3.0 for ABTS and at 6.0 for syringaldazine and the enzyme is stable up to pH 10. The UV/vis spectrum of the laccase-related enzyme is non-typical for laccases and metal content analysis revealed that the enzyme contains only a single copper atom per enzyme molecule. This suggests that this enzyme could be related to the group of the so-called "white" laccases, however, no zinc or any other metal ion could be detected in this enzyme, suggesting that the enzyme is a unique laccase-related enzyme. Comparison of the bleaching activity of the whole fungus with that of the isolated laccase-related enzyme showed that this enzyme is the major bleaching enzyme produced by this Marasmius sp. strain and was able to bleach violet, red, orange and yellow dyes in addition to a number of blue dyes.

Generation of protein-derived redox cofactors by posttranslational modification

Redox enzymes which catalyze the oxidation and reduction of substrates are ubiquitous in nature. These enzymes typically possess exogenous cofactors to allow them to perform catalytic functions which cannot be accomplished using only amino acid residues. It is now evident that nature also employs an alternative strategy of generating catalytic and redox-active sites in proteins by posttranslational modification of amino acid residues. This review describes the structures and functions of several of these protein-derived cofactors and the diverse mechanisms of posttranslational modification through which they are generated.

Uncovering novel biochemistry in the mechanism of tryptophan tryptophylquinone cofactor biosynthesis

Catalytic quinone cofactors derived from post-translational modification of amino acid residues within the enzyme polypeptide have roles in a variety of biological processes ranging from metabolism in bacteria to inflammation and connective tissue maturation in humans. In recent years, studies of the biosynthesis of one of these cofactors, tryptophan tryptophylquinone (TTQ), have provided examples of novel chemistry that is required for the generation of these protein-derived cofactors. A novel c-type diheme enzyme, MauG, catalyzes a six-electron oxidation that completes TTQ biosynthesis in a 119-kDa protein substrate. The post-translational modification reactions proceed via an unprecedented Fe(V) equivalent catalytic intermediate comprising two hemes; one an Fe(IV)=O and the other a six-coordinate Fe(IV) with axial ligands provided by amino acid residues. This high-valent diheme species is an alternative to Compound I, an Fe(IV)=O heme with a porphyrin or amino acid cation radical, which is typically the reactive intermediate of heme-dependent oxygenases and peroxidases.