Mechanistic implications of the ternary complex structural models for the photoenzyme protochlorophyllide oxidoreductase.

The photoenzyme protochlorophyllide oxidoreductase (POR) is an important enzyme for understanding biological H-transfer mechanisms. It uses light to catalyse the reduction of protochlorophyllide to chlorophyllide, a key step in chlorophyll biosynthesis. Although a wealth of spectroscopic data have provided crucial mechanistic insight, a structural rationale for POR photocatalysis has proved challenging and remains hotly debated. Recent structural models of the ternary enzyme-substrate complex, derived from crystal and electron microscopy data, show differences in the orientation of the protochlorophyllide substrate and the architecture of the POR active site, with significant implications for the catalytic mechanism. Here, we use a combination of computational and experimental approaches to investigate the compatibility of each structural model with the hypothesised reaction mechanisms and propose an alternative structural model for the cyanobacterial POR ternary complex. We show that a strictly conserved tyrosine, previously proposed to act as the proton donor in POR photocatalysis, is unlikely to be involved in this step of the reaction but is crucial for Pchlide binding. Instead, an active site cysteine is important for both hydride and proton transfer reactions in POR and is proposed to act as the proton donor, either directly or through a water-mediated network. Moreover, a conserved glutamine is important for Pchlide binding and ensuring efficient photochemistry by tuning its electronic properties, likely by interacting with the central Mg atom of the substrate. This optimal 'binding pose' for the POR ternary enzyme-substrate complex illustrates how light energy can be harnessed to facilitate enzyme catalysis by this unique enzyme.

Revealing protonation states and tracking substrate in serine hydroxymethyltransferase with room-temperature X-ray and neutron crystallography.

Pyridoxal 5'-phosphate (PLP)-dependent enzymes utilize a vitamin B6-derived cofactor to perform a myriad of chemical transformations on amino acids and other small molecules. Some PLP-dependent enzymes, such as serine hydroxymethyltransferase (SHMT), are promising drug targets for the design of small-molecule antimicrobials and anticancer therapeutics, while others have been used to synthesize pharmaceutical building blocks. Understanding PLP-dependent catalysis and the reaction specificity is crucial to advance structure-assisted drug design and enzyme engineering. Here we report the direct determination of the protonation states in the active site of Thermus thermophilus SHMT (TthSHMT) in the internal aldimine state using room-temperature joint X-ray/neutron crystallography. Conserved active site architecture of the model enzyme TthSHMT and of human mitochondrial SHMT (hSHMT2) were compared by obtaining a room-temperature X-ray structure of hSHMT2, suggesting identical protonation states in the human enzyme. The amino acid substrate serine pathway through the TthSHMT active site cavity was tracked, revealing the peripheral and cationic binding sites that correspond to the pre-Michaelis and pseudo-Michaelis complexes, respectively. At the peripheral binding site, the substrate is bound in the zwitterionic form. By analyzing the observed protonation states, Glu53, but not His residues, is proposed as the general base catalyst, orchestrating the retro-aldol transformation of L-serine into glycine.

Active site serine-193 modulates activity of human aromatic amino acid decarboxylase.

Aromatic amino acid decarboxylase is a pyridoxal 5'-phosphate-dependent enzyme responsible for the synthesis of the neurotransmitters, dopamine and serotonin. Here, by a combination of bioinformatic predictions and analyses, phosphorylation assays, spectroscopic investigations and activity measurements, we determined that Ser-193, a conserved residue located at the active site, can be phosphorylated, increasing catalytic efficiency. In order to determine the molecular basis for this functional improvement, we determined the structural and kinetic properties of the site-directed variants S193A, S193D and S193E. While S193A retains 27% of the catalytic efficiency of wild-type, the two acidic side chain variants are impaired in catalysis with efficiencies of about 0.15% with respect to the wild-type. Thus, even if located at the active site, Ser-193 is not essential for enzyme activity. We advance the idea that this residue is fundamental for the correct architecture of the active site in terms of network of interactions triggering catalysis. This role has been compared with the properties of the Ser-194 of the highly homologous enzyme histidine decarboxylase whose catalytic loop is visible in the spatial structure, allowing us to propose the validation for the effect of the phosphorylation. The effect could be interesting for AADC deficiency, a rare monogenic disease, whose broad clinical phenotype could be also related to post translational AADC modifications.

Characterization of aminoacrylate intermediates of pyridoxal-5'-phosphate dependent enzymes.

Pyridoxal-5'-phosphate (PLP) Schiff's bases of 2-aminoacrylate are intermediates in ß-elimination and ß-substitution reaction of PLP-dependent enzymes. These enzymes are found in two major families, the α-, or aminotransferase, superfamily, and the ß-family. While the α-family enzymes primarily catalyze ß-eliminations, the ß-family enzymes catalyze both ß-elimination and ß-substitution reactions. Tyrosine phenol-lyase (TPL), which catalyzes the reversible elimination of phenol from l-tyrosine, is an example of an α-family enzyme. Tryptophan synthase catalyzes the irreversible formation of l-tryptophan from l-serine and indole, and is an example of a ß-family enzyme. The identification and characterization of aminoacrylate intermediates in the reactions of both of these enzymes is discussed. The use of UV-visible absorption and fluorescence spectroscopy, X-ray and neutron crystallography, and NMR spectroscopy to identify aminoacrylate intermediates in these and other PLP enzymes is presented.

The Y430F mutant of Salmonella d-ornithine/d-lysine decarboxylase has altered stereospecificity and a putrescine allosteric activation site.

Tyrosine-430 of d-ornithine/d-lysine decarboxylase (DOKDC) is located in the active site, and was suggested to be responsible for the D-stereospecificity of the enzyme. We have prepared the Y430F mutant form of Salmonella enterica serovar typhimurium DOKDC and evaluated its catalytic activity with D- and l-lysine and ornithine. The kinetic results show that the Y430F mutant has measurable decarboxylase activity with both D- and l-lysine and ornithine, which wild type DOKDC does not. Spectroscopic experiments show that these amino acids bind to form external aldimine complexes with the pyridoxal-5'-phosphate with λmax = 425 nm. In addition, we have obtained crystal structures of Y430F DOKDC bound to HEPES, putrescine, d-ornithine, d-lysine, and d-arginine. The d-amino acids bind in the crystals to form equilibrium mixtures of gem-diamine and external aldimine complexes. Furthermore, the crystal structures reveal an unexpected allosteric product activator site for putrescine located on the 2-fold axis between the two active sites. Putrescine binds by donating hydrogen bonds from the ammonium groups to Asp-361 and Gln-358 in the specificity helix of both chains. Addition of 0.1-1 mM putrescine eliminates the lag in steady state kinetics and abolishes the sigmoid kinetics. The catalytic loop was modeled with AlphaFold2, and the model shows that Glu-181 can form additional hydrogen bonds with the bound putrescine, likely stabilizing the catalytic closed conformation.

His-163 is a stereospecific proton donor in the mechanism of d-glucosaminate-6-phosphate ammonia-lyase.

d-Glucosaminate-6-phosphate ammonia-lyase (DGL) catalyzes the conversion of d-glucosaminate-6-phosphate to 2-keto-3-deoxyglutarate-6-phosphate, with stereospecific protonation of C-3 of the product. The crystal structure of DGL showed that His-163 could serve as the proton donor. H163A mutant DGL is fully active in the steady-state reaction, and the pre-steady-state kinetics are very similar to those of wild-type DGL. However, H163A DGL accumulates a transient intermediate with λmax at 293 nm during the reaction that is not seen with wild-type DGL. Furthermore, NMR analysis of the reaction of H163A DGL in D2 O shows that the product is a mixture of deuterated diastereomers at C-3. These results establish that His-163 is the proton donor in the reaction mechanism of DGL.

M379A Mutant Tyrosine Phenol-lyase from Citrobacter freundii Has Altered Conformational Dynamics.

The M379A mutant of Citrobacter freundii tyrosine phenol-lyase (TPL) has been prepared. M379A TPL is a robust catalyst to prepare a number of tyrosines substituted at the 3-position with bulky groups that cannot be made with wild type TPL. The three dimensional structures of M379A TPL complexed with L-methionine and 3-bromo-DL-phenylalanine have been determined by X-ray crystallography. Methionine is bound as a quinonoid complex in a closed active site in 3 of 4 chains of homotetrameric M379A TPL. M379A TPL reacts with L-methionine about 8-fold slower than wild type TPL. The temperature dependence shows that the slower reaction is due to less positive activation entropy. The structure of the M379A TPL complex of 3-bromo-DL-phenylalanine has a quinonoid complex in two subunits, with an open active site conformation. The effects of the M379A mutation on TPL suggest that the mutant enzyme has altered the conformational dynamics of the active site.

Crystallographic snapshots of ternary complexes of thermophilic secondary alcohol dehydrogenase from Thermoanaerobacter pseudoethanolicus reveal the dynamics of ligand exchange and the proton relay network.

Three-dimensional structures of I86A and C295A mutant secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter pseudoethanolicus were determined by x-ray crystallography. The tetrameric structure of C295A-SADH soaked with NADP+ and dimethyl sulfoxide (DMSO) was determined to 1.85 Å with an Rfree of 0.225. DMSO is bound to the tetrahedral zinc in each subunit, with ligands from SG of Cys-37, NE2 of His-59, and OD2 of Asp-150. The nicotinamide ring of NADP is hydrogen-bonded to the N of Ala-295 and the O of Val-265 and Gly-293. The O of DMSO is connected to a network of hydrogen bonds with OG of Ser-39, the 3'-OH of NADP, and ND1 of His-42. The structure of I86A-SADH soaked with 2-pentanol and NADP+ contains (R)-2-pentanol bound in each subunit, ligated to the tetrahedral zinc, and connected to the proton relay network. The structure of I86A-SADH soaked with 3-methylcyclohexanol and NADP+ has alcohol bound in three subunits. Two of the sites have the alcohol ligated to the zinc in an axial position, with OE2 of Glu-60 in the other axial position of a trigonal bipyramidal complex. One site has 3-methylcyclohexanol bound noncovalently, with the zinc in an inverted tetrahedral geometry with Glu-60. The fourth site also has the zinc in a trigonal bipyramidal complex with axial Glu-60 and water ligands. These structures demonstrate that ligand exchange of SADH involves pentacoordinate and inverted zinc complexes with Glu-60. Furthermore, we see a network of hydrogen bonds connecting the substrate oxygen to the external solvent that is likely to play a role in the mechanism of SADH.

Predicting relapse or recurrence of depression: systematic review of prognostic models.

BACKGROUND: Relapse and recurrence of depression are common, contributing to the overall burden of depression globally. Accurate prediction of relapse or recurrence while patients are well would allow the identification of high-risk individuals and may effectively guide the allocation of interventions to prevent relapse and recurrence. AIMS: To review prognostic models developed to predict the risk of relapse, recurrence, sustained remission, or recovery in adults with remitted major depressive disorder. METHOD: We searched the Cochrane Library (current issue); Ovid MEDLINE (1946 onwards); Ovid Embase (1980 onwards); Ovid PsycINFO (1806 onwards); and Web of Science (1900 onwards) up to May 2021. We included development and external validation studies of multivariable prognostic models. We assessed risk of bias of included studies using the Prediction model risk of bias assessment tool (PROBAST). RESULTS: We identified 12 eligible prognostic model studies (11 unique prognostic models): 8 model development-only studies, 3 model development and external validation studies and 1 external validation-only study. Multiple estimates of performance measures were not available and meta-analysis was therefore not necessary. Eleven out of the 12 included studies were assessed as being at high overall risk of bias and none examined clinical utility. CONCLUSIONS: Due to high risk of bias of the included studies, poor predictive performance and limited external validation of the models identified, presently available clinical prediction models for relapse and recurrence of depression are not yet sufficiently developed for deploying in clinical settings. There is a need for improved prognosis research in this clinical area and future studies should conform to best practice methodological and reporting guidelines.

The Kynurenine Pathway and Kynurenine 3-Monooxygenase Inhibitors.

Under normal physiological conditions, the kynurenine pathway (KP) plays a critical role in generating cellular energy and catabolizing tryptophan. Under inflammatory conditions, however, there is an upregulation of the KP enzymes, particularly kynurenine 3-monooxygenase (KMO). KMO has garnered much attention due to its production of toxic metabolites that have been implicated in many diseases and disorders. With many of these illnesses having an inadequate or modest treatment, there exists a need to develop KMO inhibitors that reduce the production of these toxic metabolites. Though prior efforts to find an appropriate KMO inhibitor were unpromising, the development of a KMO crystal structure has provided the opportunity for a rational structure-based design in the development of inhibitors. Therefore, the purpose of this review is to describe the kynurenine pathway, the kynurenine 3-monooxygenase enzyme, and KMO inhibitors and their potential candidacy for clinical use.

Using Evidence-Based Medicine to Support Clinical Decision-Making in RMS.

The foundations of evidence-based practice are the triad of patient values and preferences, healthcare professional experience, and best available evidence, used together to inform clinical decision-making. Within the field of rhabdomyosarcoma, collaborative groups such as the European Paediatric Soft Tissue Sarcoma Group (EpSSG) have worked to develop evidence to support this process. We have explored many of the key research developments within this review, including patient and public involvement, decision-making research, research into areas other than drug development, core outcome sets, reporting and dissemination of research, evidence synthesis, guideline development and clinical decision rules, research of research methodologies, and supporting research in RMS.

Structure and Mechanism of d-Glucosaminate-6-phosphate Ammonia-lyase: A Novel Octameric Assembly for a Pyridoxal 5'-Phosphate-Dependent Enzyme, and Unprecedented Stereochemical Inversion in the Elimination Reaction of a d-Amino Acid.

d-Glucosaminate-6-phosphate ammonia-lyase (DGL) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that produces 2-keto-3-deoxygluconate 6-phosphate (KDG-6-P) in the metabolism of d-glucosaminic acid by Salmonella enterica serovar typhimurium. We have determined the crystal structure of DGL by SAD phasing with selenomethionine to a resolution of 2.58 Å. The sequence has very low identity with most other members of the aminotransferase (AT) superfamily. The structure forms an octameric assembly as a tetramer of dimers that has not been observed previously in the AT superfamily. PLP is covalently bound as a Schiff base to Lys-213 in the catalytic dimer at the interface of two monomers. The structure lacks the conserved arginine that binds the α-carboxylate of the substrate in most members of the AT superfamily. However, there is a cluster of arginines in the small domain that likely serves as a binding site for the phosphate of the substrate. The deamination reaction performed in D2O gives a KDG-6-P product stereospecifically deuterated at C3; thus, the mechanism must involve an enamine intermediate that is protonated by the enzyme before product release. Nuclear magnetic resonance (NMR) analysis demonstrates that the deuterium is located in the pro-R position in the product, showing that the elimination of water takes place with inversion of configuration at C3, which is unprecedented for a PLP-dependent dehydratase/deaminase. On the basis of the crystal structure and the NMR data, a reaction mechanism for DGL is proposed.

Prognostic models for predicting relapse or recurrence of major depressive disorder in adults.

BACKGROUND: Relapse (the re-emergence of depressive symptoms after some level of improvement but preceding recovery) and recurrence (onset of a new depressive episode after recovery) are common in depression, lead to worse outcomes and quality of life for patients and exert a high economic cost on society. Outcomes can be predicted by using multivariable prognostic models, which use information about several predictors to produce an individualised risk estimate. The ability to accurately predict relapse or recurrence while patients are well (in remission) would allow the identification of high-risk individuals and may improve overall treatment outcomes for patients by enabling more efficient allocation of interventions to prevent relapse and recurrence. OBJECTIVES: To summarise the predictive performance of prognostic models developed to predict the risk of relapse, recurrence, sustained remission or recovery in adults with major depressive disorder who meet criteria for remission or recovery. SEARCH METHODS: We searched the Cochrane Library (current issue); Ovid MEDLINE (1946 onwards); Ovid Embase (1980 onwards); Ovid PsycINFO (1806 onwards); and Web of Science (1900 onwards) up to May 2020. We also searched sources of grey literature, screened the reference lists of included studies and performed a forward citation search. There were no restrictions applied to the searches by date, language or publication status . SELECTION CRITERIA: We included development and external validation (testing model performance in data separate from the development data) studies of any multivariable prognostic models (including two or more predictors) to predict relapse, recurrence, sustained remission, or recovery in adults (aged 18 years and over) with remitted depression, in any clinical setting. We included all study designs and accepted all definitions of relapse, recurrence and other related outcomes. We did not specify a comparator prognostic model. DATA COLLECTION AND ANALYSIS: Two review authors independently screened references; extracted data (using a template based on the CHecklist for critical Appraisal and data extraction for systematic Reviews of prediction Modelling Studies (CHARMS)); and assessed risks of bias of included studies (using the Prediction model Risk Of Bias ASsessment Tool (PROBAST)). We referred any disagreements to a third independent review author. Where we found sufficient (10 or more) external validation studies of an individual model, we planned to perform a meta-analysis of its predictive performance, specifically with respect to its calibration (how well the predicted probabilities match the observed proportions of individuals that experience the outcome) and discrimination (the ability of the model to differentiate between those with and without the outcome). Recommendations could not be qualified using the GRADE system, as guidance is not yet available for prognostic model reviews. MAIN RESULTS: We identified 11 eligible prognostic model studies (10 unique prognostic models). Seven were model development studies; three were model development and external validation studies; and one was an external validation-only study. Multiple estimates of performance measures were not available for any of the models and, meta-analysis was therefore not possible. Ten out of the 11 included studies were assessed as being at high overall risk of bias. Common weaknesses included insufficient sample size, inappropriate handling of missing data and lack of information about discrimination and calibration. One paper (Klein 2018) was at low overall risk of bias and presented a prognostic model including the following predictors: number of previous depressive episodes, residual depressive symptoms and severity of the last depressive episode. The external predictive performance of this model was poor (C-statistic 0.59; calibration slope 0.56; confidence intervals not reported). None of the identified studies examined the clinical utility (net benefit) of the developed model. AUTHORS' CONCLUSIONS: Of the 10 prognostic models identified (across 11 studies), only four underwent external validation. Most of the studies (n = 10) were assessed as being at high overall risk of bias, and the one study that was at low risk of bias presented a model with poor predictive performance. There is a need for improved prognostic research in this clinical area, with future studies conforming to current best practice recommendations for prognostic model development/validation and reporting findings in line with the Transparent Reporting of a multivariable prediction model for Individual Prognosis Or Diagnosis (TRIPOD) statement.

New cases that expand the genotypic and phenotypic spectrum of Congenital NAD Deficiency Disorder.

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme involved in over 400 cellular reactions. During embryogenesis, mammals synthesize NAD de novo from dietary l -tryptophan via the kynurenine pathway. Biallelic, inactivating variants in three genes encoding enzymes of this biosynthesis pathway (KYNU, HAAO, and NADSYN1) disrupt NAD synthesis and have been identified in patients with multiple malformations of the heart, kidney, vertebrae, and limbs; these patients have Congenital NAD Deficiency Disorder HAAO and four families with biallelic variants in KYNU. These patients present similarly with multiple malformations of the heart, kidney, vertebrae, and limbs, of variable severity. We show that each variant identified in these patients results in loss-of-function, revealed by a significant reduction in NAD levels via yeast genetic complementation assays. For the first time, missense mutations are identified as a cause of malformation and shown to disrupt enzyme function. These missense and frameshift variants cause moderate to severe NAD deficiency in yeast, analogous to insufficient synthesized NAD in patients. We hereby expand the genotypic and corresponding phenotypic spectrum of Congenital NAD Deficiency Disorder.

Secondary Alcohol Dehydrogenases from Thermoanaerobacter pseudoethanolicus and Thermoanaerobacter brockii as Robust Catalysts.

Alcohol dehydrogenases (ADHs) are an important type of enzyme that have significant applications as biocatalysts. Secondary ADHs from Thermoanaerobacter pseudoethanolicus (TeSADH) and Thermoanaerobacter brockii (TbSADH) are well-known as robust catalysts. However, like most other ADHs, these enzymes suffer from their high substrate specificities (i. e., limited substrate scope), which to some extent restricts their use as biocatalysts. This minireview discusses recent efforts to expand the substrate scope and tune the enantioselectivity of TeSADH and TbSADH by using site-directed mutagenesis and directed evolution. Various examples of asymmetric synthesis of optically active alcohols using both enzymes are highlighted. Moreover, the unique thermal stability and organic solvent tolerance of these enzymes is illustrated by their concurrent inclusion with other interesting reactions to synthesize optically active alcohols and amines. For instance, TeSADH has been used in quantitative non-stereoselective oxidation of alcohols to deracemize alcohols via cyclic deracemization and in the racemization of enantiopure alcohols to accomplish a bienzymatic dynamic kinetic resolution.

Structural Basis of the Stereochemistry of Inhibition of Tryptophan Synthase by Tryptophan and Derivatives.

We have examined the reaction of Salmonella enterica serovar typhimurium tryptophan (Trp) synthase α2ß2 complex with l-Trp, d-Trp, oxindolyl-l-alanine (OIA), and dioxindolyl-l-alanine (DOA) in the presence of disodium (dl)-α-glycerol phosphate (GP), using stopped-flow spectrophotometry and X-ray crystallography. All structures contained the d-isomer of GP bound at the α-active site. (3S)-OIA reacts with the pyridoxal-5'-phosphate (PLP) of Trp synthase to form a mixture of external aldimine and quinonoid complexes. The α-carboxylate of OIA rotates about 90° to become planar with the PLP when the quinonoid complex is formed, resulting in a conformational change in the loop of residues 110-115. The COMM domain of the Trp synthase-OIA complex is found as a mixture of two conformations. The (3R)-diastereomer of DOA binds about 5-fold more tightly than (3S)-OIA and also forms a mixture of aldimine and quinonoid complexes. DOA forms an additional H-bond between the 3-OH of DOA and ßLys-87. l-Trp does not form a covalent complex with the PLP of Trp synthase. However, d-Trp forms a mixture of two external aldimine complexes which differ in the orientation of the α-carboxylate. In one conformation, the α-carboxylate is in the plane of the PLP, while in the other conformation, the α-carboxylate is perpendicular to the PLP plane. These results confirm that the stereochemistry of the transient indolenine quinonoid intermediate in the mechanism of Trp synthase is (3S) and demonstrate the linkage between aldimine and quinonoid reaction intermediates in the ß-active site and allosteric communications with the α-active site.

Severity of COVID-19 in children with cancer: Report from the United Kingdom Paediatric Coronavirus Cancer Monitoring Project.

BACKGROUND: Children with cancer are frequently immunocompromised. While children are generally thought to be at less risk of severe SARS-CoV-2 infection than adults, comprehensive population-based evidence for the risk in children with cancer is unavailable. We aimed to produce evidence of the incidence and outcomes from SARS-CoV-2 in children with cancer attending all hospitals treating this population across the UK. METHODS: Retrospective and prospective observational study of all children in the UK under 16 diagnosed with cancer through data collection from all hospitals providing cancer care to this population. Eligible patients tested positive for SARS-CoV-2 on reverse transcription polymerase chain reaction (RT-PCR). The primary end-point was death, discharge or end of active care for COVID-19 for those remaining in hospital. RESULTS: Between 12 March 2020 and 31 July 2020, 54 cases were identified: 15 (28%) were asymptomatic, 34 (63%) had mild infections and 5 (10%) moderate, severe or critical infections. No patients died and only three patients required intensive care support due to COVID-19. Estimated incidence of hospital identified SARS-CoV-2 infection in children with cancer under 16 was 3%. CONCLUSIONS: Children with cancer with SARS-CoV-2 infection do not appear at increased risk of severe infection compared to the general paediatric population. This is reassuring and supports the continued delivery of standard treatment.

Oxygen reactivity with pyridoxal 5'-phosphate enzymes: biochemical implications and functional relevance.

The versatility of reactions catalyzed by pyridoxal 5'-phosphate (PLP) enzymes is largely due to the chemistry of their extraordinary catalyst. PLP is necessary for many reactions involving amino acids. Reaction specificity is controlled by the orientation of the external aldimine intermediate that is formed upon addition of the amino acidic substrate to the coenzyme. The breakage of a specific bond of the external aldimine gives rise to a carbanionic intermediate. From this point, the different reaction pathways diverge leading to multiple activities: transamination, decarboxylation, racemization, elimination, and synthesis. A significant novelty appeared approximately 30 years ago when it was reported that some PLP-dependent decarboxylases are able to consume molecular oxygen transforming an amino acid into a carbonyl compound. These side paracatalytic reactions could be particularly relevant for human health, also considering that some of these enzymes are responsible for the synthesis of important neurotransmitters such as γ-aminobutyric acid, dopamine, and serotonin, whose dysregulation under oxidative conditions could have important implications in neurodegenerative states. However, the reactivity of PLP enzymes with dioxygen is not confined to mammals/animals. In fact, some plant PLP decarboxylases have been reported to catalyze oxidative reactions producing carbonyl compounds. Moreover, other recent reports revealed the existence of new oxidase activities catalyzed by new PLP enzymes, MppP, RohP, Ind4, CcbF, PvdN, Cap15, and CuaB. These PLP enzymes belong to the bacterial and fungal kingdoms and are present in organisms synthesizing bioactive compounds. These new PLP activities are not paracatalytic and could only scratch the surface on a wider and unexpected catalytic capability of PLP enzymes.