The cation-π interaction between Lys53 and the flavin of fructosamine oxidase (FAOX-II) is critical for activity

The family of sarcosine oxidases: Same reaction, different products

The subfamily of sarcosine oxidase is a set of enzymes within the larger family of amine oxidases. It is ubiquitously distributed among different kingdoms of life. The member enzymes catalyze the oxidization of an N-methyl amine bond of amino acids to yield unstable imine species that undergo subsequent spontaneous non-enzymatic reactions, forming an array of different products. These products range from demethylated simple species to complex alkaloids. The enzymes belonging to the sarcosine oxidase family, namely, monomeric and heterotetrameric sarcosine oxidase, l-pipecolate oxidase, N-methyltryptophan oxidase, NikD, l-proline dehydrogenase, FsqB, fructosamine oxidase and saccharopine oxidase have unique features differentiating them from other amine oxidases. This review highlights the key attributes of the sarcosine oxidase family enzymes, in terms of their substrate binding motif, type of oxidation reaction mediated and FAD regeneration, to define the boundaries of this group and demarcate these enzymes from other amine oxidase families.

The vast repertoire of carbohydrate oxidases: An overview

Carbohydrates are widely abundant molecules present in a variety of forms. For their biosynthesis and modification, nature has evolved a plethora of carbohydrate-acting enzymes. Many of these enzymes are of particular interest for biotechnological applications, where they can be used as biocatalysts or biosensors. Among the enzymes catalysing conversions of carbohydrates are the carbohydrate oxidases. These oxidative enzymes belong to different structural families and use different cofactors to perform the oxidation reaction of CH-OH bonds in carbohydrates. The variety of carbohydrate oxidases available in nature reflects their specificity towards different sugars and selectivity of the oxidation site. Thanks to their properties, carbohydrate oxidases have received a lot of attention in basic and applied research, such that nowadays their role in biotechnological processes is of paramount importance. In this review we provide an overview of the available knowledge concerning the known carbohydrate oxidases. The oxidases are first classified according to their structural features. After a description on their mechanism of action, substrate acceptance and characterisation, we report on the engineering of the different carbohydrate oxidases to enhance their employment in biocatalysis and biotechnology. In the last part of the review we highlight some practical applications for which such enzymes have been exploited.

The Transformative Possibilities of the Microbiota and Mycobiota for Health, Disease, Aging, and Technological Innovation

The gut microbiota is extremely important for the health of the host across its lifespan.Recent studies have elucidated connections between the gut microbiota and neurological diseaseand disorders such as depression, anxiety, Alzheimer's disease (AD), autism, and a host of otherbrain illnesses. Dysbiosis of the normal gut flora can have negative consequences for humans,especially throughout key periods during our lifespan as the gut microbes change with age in bothphenotype and number of bacterial species. Neurologic diseases, mental disorders, and euthymicstates are influenced by alterations in the metabolites produced by gut microbial milieu. Weintroduce a new concept, namely, the mycobiota and microbiota-gut-brain neuroendocrine axis anddiscuss co-metabolism with emphasis on means to influence or correct disruptions to normal gutflora throughout the lifespan from early development to old age. These changes involveinflammation and involve the permeability of barriers, such as the intestine blood barrier, the blood⁻brain barrier, and others. The mycobiota and microbiota⁻gut⁻brain axis offer new research horizonsand represents a great potential target for new therapeutics, including approaches based aroundinflammatory disruptive process, genetically engineered drug delivery systems, diseased cellculling "kill switches", phage-like therapies, medicinal chemistry, or microbial parabiosis to namea few.

X-ray structures of fructosyl peptide oxidases revealing residues responsible for gating oxygen access in the oxidative half reaction

Current enzymatic systems for quantifying glycated hemoglobin are based on the FAD-containing enzyme fructosyl peptide oxidase (FPOX). FPOX has substrate specificity for fructosyl-^α N-valyl-histidine derived from proteolytic digestion of the N-terminus of the HbA1c β-chain. This study reports the X-ray structures of the wild-type and Asn56Ala (N56A) mutant of Phaeosphaeria nodorum fructosyl peptide oxidase (PnFPOX) to elucidate the residues responsible for the oxidative half-reaction. N56A showed decreased oxidase activity compared to the wild -type, while its dye-mediated dehydrogenase activity was higher than that of wild type. In wild-type PnFPOX, Asn56 forms a hydrogen bond with Lys274, thereby preventing it from forming a salt bridge with Asp54. By contrast, Lys274 of PnFPOX N56A moves toward Asp54, and they approach each other to form a salt bridge at a distance of 2.92-3.35 Å. Site-directed mutagenesis studies and protein channel analysis suggest that Asp54 assists in accepting oxygen properly at the position of the bound water molecule in the main oxygen channel. These results reveal that Asn56 in PnFPOX is essential for maintaining an effective oxygen accession path, and support the role of Asp54 as a gate keeper that cooperates with Lys274 to enable oxygen to reach the active site properly.

Effects of the aromatic substitution pattern in cation-π sandwich complexes

A computational study investigating the effects of the aromatic substitution pattern on the structure and binding energies of cation-π sandwich complexes is reported. The correlation between the binding energies (Ebind) and Hammett substituent constants is approximately the same as what is observed for cation-π half-sandwich complexes. For cation-π sandwich complexes where both aromatics contain substituents the issue of relative conformation is a possible factor in the strength of the binding; however, the work presented here shows the Ebind values are approximately the same regardless of the relative conformation of the two substituted aromatics. Finally, recent computational work has shown conflicting results on whether cation-π sandwich Ebind values (Ebind,S) are approximately equal to twice the respective half-sandwich Ebind values (Ebind,HS), or if cation-π sandwich Ebind,S values are less than double the respective half-sandwich Ebind,HS values. The work presented here shows that for cation-π sandwich complexes involving substituted aromatics the Ebind,S values are less than twice the respective half-sandwich Ebind,HS values, and this is termed nonadditive. The extent to which the cation-π sandwich complexes investigated here are nonadditive is greater for B3LYP calculated values than for MP2 calculated values and for sandwich complexes with electron-donating substituents than those with electron-withdrawing groups.

Oxygen reactivity in flavoenzymes: context matters

Many flavoenzymes--oxidases and monooxygenases--react faster with oxygen than free flavins do. There are many ideas on how enzymes cause this. Recent work has focused on the importance of a positive charge near N5 of the reduced flavin. Fructosamine oxidase has a lysine near N5 of its flavin. We measured a rate constant of 1.6 × 10(5) M(-1) s(-1) for its reaction with oxygen. The Lys276Met mutant reacted with a rate constant of 291 M(-1) s(-1), suggesting an important role for this lysine in oxygen activation. The dihydroorotate dehydrogenases from E. coli and L. lactis also have a lysine near N5 of the flavin. They react with O(2) with rate constants of 6.2 × 10(4) and 3.0 × 10(3) M(-1) s(-1), respectively. The Lys66Met and Lys43Met mutant enzymes react with rate constants that are nearly the same as those for the wild-type enzymes, demonstrating that simply placing a positive charge near N5 of the flavin does not guarantee increased oxygen reactivity. Our results show that the lysine near N5 does not exert an effect without an appropriate context; evolution did not find only one mechanism for activating the reaction of flavins with O(2).