Two Different Quinohemoprotein Amine Dehydrogenases Initiate Anaerobic Degradation of Aromatic Amines in Aromatoleum aromaticum EbN1.

Aromatic amines like 2-phenylethylamine (2-PEA) and benzylamine (BAm) have been identified as novel growth substrates of the betaproteobacterium Aromatoleum aromaticum EbN1, which degrades a wide variety of aromatic compounds in the absence of oxygen under denitrifying growth conditions. The catabolic pathway of these amines was identified, starting with their oxidative deamination to the corresponding aldehydes, which are then further degraded via the enzymes of the phenylalanine or benzyl alcohol metabolic pathways. Two different periplasmic quinohemoprotein amine dehydrogenases involved in 2-PEA or BAm metabolism were identified and characterized. Both enzymes consist of three subunits, contain two heme c cofactors in their α-subunits, and exhibit extensive processing of their γ-subunits, generating four intramolecular thioether bonds and a cysteine tryptophylquinone (CTQ) cofactor. One of the enzymes was present in cells grown with 2-PEA or other substrates, showed an α2ß2γ2 composition, and had a rather broad substrate spectrum, which included 2-PEA, BAm, tyramine, and 1-butylamine. In contrast, the other enzyme was specifically induced in BAm-grown cells, showing an αßγ composition and activity only with BAm and 2-PEA. Since the former enzyme showed the highest catalytic efficiency with 2-PEA and the latter with BAm, they were designated 2-PEADH and benzylamine dehydrogenase (BAmDH). The catalytic properties and inhibition patterns of 2-PEADH and BAmDH showed considerable differences and were compared to previously characterized quinohemoproteins of the same enzyme family.IMPORTANCE The known substrate spectrum of A. aromaticum EbN1 is expanded toward aromatic amines, which are metabolized as sole substrates coupled to denitrification. The characterization of the two quinohemoprotein isoenzymes involved in degrading either 2-PEA or BAm expands the knowledge of this enzyme family and establishes for the first time that the necessary maturation of their quinoid CTQ cofactors does not require the presence of molecular oxygen. Moreover, the study revealed a highly interesting regulatory phenomenon, suggesting that growth with BAm leads to a complete replacement of 2-PEADH by BAmDH, which has considerably different catalytic and inhibition properties.

Characterization of an Aldehyde Oxidoreductase From the Mesophilic Bacterium Aromatoleum aromaticum EbN1, a Member of a New Subfamily of Tungsten-Containing Enzymes.

The biochemical properties of a new tungsten-containing aldehyde oxidoreductase from the mesophilic betaproteobacterium Aromatoleum aromaticum EbN1 (AOR Aa ) are presented in this study. The enzyme was purified from phenylalanine-grown cells of an overexpressing mutant lacking the gene for an aldehyde dehydrogenase normally involved in anaerobic phenylalanine degradation. AOR Aa catalyzes the oxidation of a broad variety of aldehydes to the respective acids with either viologen dyes or NAD+ as electron acceptors. In contrast to previously known AORs, AOR Aa is a heterohexameric protein consisting of three different subunits, a large subunit containing the W-cofactor and an Fe-S cluster, a small subunit containing four Fe-S clusters, and a medium subunit containing an FAD cofactor. The presence of the expected cofactors have been confirmed by elemental analysis and spectrophotometric methods. AOR Aa has a pH optimum of 8.0, a temperature optimum of 40°C and is completely inactive at 50°C. Compared to archaeal AORs, AOR Aa is remarkably resistant against exposure to air, exhibiting a half-life time of 1 h as purified enzyme and being completely unaffected in cell extracts. Kinetic parameters of AOR Aa have been obtained for the oxidation of one aliphatic and two aromatic aldehydes, resulting in about twofold higher k cat values with benzyl viologen than with NAD+ as electron acceptor. Finally, we obtained evidence that AOR Aa is also catalyzing the reverse reaction, reduction of benzoate to benzaldehyde, albeit at very low rates and under conditions strongly favoring acid reduction, e.g., low pH and using Ti(III) citrate as electron donor of very low redox potential. AOR Aa appears to be a prototype of a new subfamily of bacterial AOR-like tungsten-enzymes, which differ from the previously known archaeal AORs mostly by their multi-subunit composition, their low sensitivity against oxygen, and the ability to use NAD+ as electron acceptor.

Changes in the composition of the upper respiratory tract microbial community in granulomatosis with polyangiitis.

Dysbiosis¸ i.e. changes in microbial composition at a mucosal interface, is implicated in the pathogenesis of many chronic inflammatory and autoimmune diseases. To assess the composition of the microbial upper respiratory tract (URT) community in patients with granulomatosis with polyangiitis (GPA), we used culture-independent high-throughput methods. In this prospective clinical study, nasal swabs were collected from patients with GPA, patients with rheumatoid arthritis (RA, disease control), and healthy controls. Nasal bacterial taxa were assessed using V3-V4 region 16S rRNA amplicon sequencing. Staphylococcus aureus, Haemophilus influenza, and entero- and rhinoviruses were detected using qPCR. Unbiased metagenomic RNA sequencing (UMERS) was performed in a subset of samples to determine the relative abundance of bacterial, fungal, and viral species. A trend toward reduced microbiome diversity was detected in GPA samples compared with healthy controls. The abundance of bacterial taxa and microbial richness were significantly decreased in GPA samples compared with RA samples. The relative abundance of bacterial families shifted, with increased Planococcaceae and decreased Moraxellaceae, Tissierellaceae, Staphylococcaceae, and Propionibacteriaceae in GPA and RA. Further, decreased abundance of Corynebacteriaceae, and Aerococcaceae was observed in GPA samples. Significantly more colonization of S. aureus was seen in the nasal microbiome of GPA compared with RA and healthy control samples. H. influenzae colonization was also observed in GPA samples. UMERS detected the presence of rhinoviral sequences in some GPA samples. Thus, our study uncovered changes in the URT microbial composition in patients with GPA and RA, suggesting that both immunosuppression and disease background affect the URT microbiome. Complex alterations of host-microbiome interactions in the URT could influence chronic endonasal inflammation in GPA.

Serum immunoglobulin G4 in giant cell arteritis and polymyalgia rheumatica.

OBJECTIVES: To date, no specific serum marker for giant cell arteritis and polymyalgia rheumatica has been established in routine practice. Therefore, the aim of this study was to examine whether immunoglobulin G4 serum concentrations could be a potential biomarker for the differentiation of both diseases. METHODS: Serum immunoglobulin G4 (IgG4) concentrations were measured in patients with giant cell arteritis (n=41) and polymyalgia rheumatica (n=27) by an in-house enzyme-linked immunosorbent assay. In the subgroup of untreated patients with disease activity (polymyalgia rheumatica n=27, giant cell arteritis n=19) additional parameters of T-helper 2 cell inflammatory responses were analysed. RESULTS: IgG4-values above the prior determined cut-off value of 1400 µg/ml in giant cell arteritis were rare and also significantly less frequent in giant cell arteritis than in polymyalgia rheumatica patients (7.3% vs. 44.4%; p<0.001). The relative risk that patients with clinical features of PMR, presenting without elevated IgG4 levels, have simultaneously GCA was 5.8 compared to those patients with elevated IgG4 levels. In untreated patients absolute counts of eosinophilic leukocytes were lower in giant cell arteritis than in polymyalgia rheumatica (p=0.002) and the cytokines interleukin-4 (p=0.013) and interleukin-10 (p=0.033) were less frequently detectable in giant cell arteritis than in polymyalgia rheumatica. CONCLUSIONS: In giant cell arteritis serum levels of IgG4 usually are within the normal range. In polymyalgia rheumatica however, increased IgG4 serum levels are frequently found. Normal IgG4 serum levels in polymyalgia rheumatica may have predictive value in identifying patients with additional, clinically non-apparent giant cell arteritis.

HLA-DPB1 as a Risk Factor for Relapse in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis: A Cohort Study.

OBJECTIVE: The antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) form a group of small-vessel vasculitides with systemic involvement. Although the etiology of AAVs remains largely unknown, both genetic and environmental factors have been implicated. Recently, certain alleles in the HLA-DPB1 region on chromosome 6 were shown to be associated with proteinase 3 (PR3)-ANCA-positive AAV but not with myeloperoxidase (MPO)-ANCA-positive AAV. The aim of this study was to investigate whether different alleles in the HLA-DPB1 region have clinical and/or prognostic implications in AAV. METHODS: One hundred seventy-four patients with a diagnosis of AAV were recruited at the Maastricht University Medical Centre between 2000 and 2009. Seventeen different HLA-DPB1 alleles were determined using the restriction fragment length polymorphism technique. A validation cohort of 170 AAV patients from the Vasculitis Centre of Luebeck/Bad Bramstedt was included. RESULTS: In the initial cohort, the distribution of HLA-DPB1 alleles was significantly different between PR3-ANCA-positive compared with MPO-ANCA-positive AAV patients, ANCA-negative AAV patients, and healthy controls. Importantly, HLA-DPB1*04:01 was present in 90% of PR3-ANCA-positive AAV patients compared with 63% of MPO-ANCA-positive AAV patients, 58% of ANCA-negative patients, and 63% of healthy controls. Patients homozygous for HLA-DPB1*04:01 had relapses more often compared with heterozygous patients and noncarrier patients. This association persisted after correction for ANCA subtype and diagnosis. In the validation cohort, patients homozygous for HLA-DPB1*04:01 and those heterozygous for HLA-DPB1*04:01 had relapses more often compared with noncarrier patients. When both patient cohorts were merged (n = 344), homozygous patients relapsed most often, followed by heterozygous patients and noncarrier patients. CONCLUSION: Carriage of HLA-DPB1*04:01 in patients with AAV is significantly associated with an increased risk of relapse compared with HLA-DPB1*04:01-negative patients, irrespective of ANCA status or clinical AAV entity.