Enzyme-cargo encapsulation peptides bind between tessellating tiles of the bacterial microcompartment shell.

Bacterial microcompartments are prokaryotic organelles comprising encapsulated enzymes within a thin protein shell. They facilitate metabolic processing including propanediol, choline, glycerol, and ethanolamine utilization, and they accelerate carbon fixation in cyanobacteria. Enzymes targeted to the inside of the microcompartment frequently possess a cargo-encapsulation peptide, but the site to which the peptide binds is unclear. We provide evidence that the encapsulation peptides bind to the hydrophobic groove formed between tessellating subunits of the shell proteins. In silico docking studies provide a compelling model of peptide binding to this prominent hydrophobic groove. This result is consistent with the now widely accepted view that the convex side of the shell oligomers faces the lumen of the microcompartment. The binding of the encapsulation peptide to the groove between tessellating shell protein tiles explains why it has been difficult to define the peptide binding site using other methods, provides a mechanism by which encapsulation-peptide bearing enzymes can promote shell assembly, and explains how the presence of cargo affects the size and shape of the bacterial microcompartment. This knowledge may be exploited in engineering microcompartments or disease prevention by hampering cargo encapsulation.

Between loss and restoration: The role of liminality in advancing theories of grief and bereavement.

A recent national survey of bereaved partners found high levels of complicated grief and psychological distress, with evidence that loneliness and isolation may contribute to these outcomes. However, the mechanisms of action for this have not been explored. To advance grief theory this paper reports analysis of the survey free-text data to examine the relationship between social support and emotional responses to bereavement. Individuals bereaved of a civil partner or spouse 6-10 months previously were identified through death registration data. 569/1945 (29 %) completed surveys were received. Of those, 311 participants (55 %) provided responses to two free-text questions which asked about their 'feelings since the death of their partner or spouse', and 'about the support around' them. Data were analysed using corpus-assisted discourse analysis and the discourse dynamics approach for figurative language. Participants described diverse emotional responses to the bereavement (e.g. sadness, anger, denial, acceptance), and the value of formal and informal bereavement support. Although many of the experiences described are accounted for in existing grief theory, some participants described a liminal experience not recognised within these theories. They felt trapped, unable to engage with loss or restoration, and unable to move forward as their planned future no longer existed. They sought out 'communitas' (solidarity in experiences), but often found support from their social networks had diminished. Metaphors were used to describe this liminality, with partner grief expressed as a dark agentic force, a monster, an abyss, and as water. The findings of this study offer original insights into experiences and trajectories of bereavement, and our understandings of prolonged or complicated grief. A novel model 'Between Loss and Restoration' is presented to include these experiences. Recognition of the place for liminality within the spectrum of grief experiences could enhance grief literacy and improve formal and informal bereavement support provision.

Communication about sexual orientation and gender between clinicians, LGBT+ people facing serious illness and their significant others: a qualitative interview study of experiences, preferences and recommendations.

BACKGROUND: Healthcare organisations have legal and ethical duties to reduce inequalities in access to healthcare services and related outcomes. However, lesbian, gay, bisexual and/or transgender (LGBT+) people continue to experience and anticipate discrimination in health and social care. Skilled communication is vital for quality person-centred care, but there is inconsistent provision of evidence-based clinician education on health needs and experiences of LGBT+ people to support this. This study aimed to identify key stakeholders' experiences, preferences and best practices for communication regarding sexual orientation, gender identity and gender history in order to reduce inequalities in healthcare. METHODS: Semistructured qualitative interviews with LGBT+ patients with serious illness, significant others and clinicians, recruited via UK-wide LGBT+ groups, two hospitals and one hospice in England. We analysed the interview data using reflexive thematic analysis. RESULTS: 74 stakeholders participated: 34 LGBT+ patients with serious illness, 13 significant others and 27 multiprofessional clinicians. Participants described key communication strategies to promote inclusive practice across three domains: (1) 'Creating positive first impressions and building rapport' were central to relationship building and enacted through routine use of inclusive language, avoiding potentially negative non-verbal signals and echoing terminology used by patients and caregivers; (2) 'Enhancing care by actively exploring and explaining the relevance of sexual orientation and gender identity', participants described the benefits of clinicians initiating these discussions, pursuing topics guided by the patient's response or expressed preferences for disclosure. Active involvement of significant others was encouraged to demonstrate recognition of the relationship; these individual level actions are underpinned by a foundation of (3) 'visible and consistent LGBT+ inclusiveness in care systems'. Although participants expressed hesitance talking about LGBT+ identities with individuals from some sociocultural and religious backgrounds, there was widespread support for institutions to adopt a standardised, LGBT+ inclusive, visibly supportive approach. CONCLUSIONS: Person-centred care can be enhanced by incorporating discussions about sexual orientation and gender identity into routine clinical practice. Inclusive language and sensitive exploration of relationships and identities are core activities. Institutions need to support clinicians through provision of adequate training, resources, inclusive monitoring systems, policies and structures. Ten inclusive communication recommendations are made based on the data.

Does the impact of bereavement vary between same and different gender partnerships? A representative national, cross-sectional study.

BACKGROUND: Data suggest poorer bereavement outcomes for lesbian, gay and bisexual people, but this has not been estimated in population-based research. This study compared bereavement outcomes for partners of same-gender and different-gender decedents. METHODS: In this population-based, cross-sectional survey of people bereaved of a civil partner or spouse 6-10 months previously, we used adjusted logistic and linear regression to investigate outcomes of interest: (1) positive screen on Inventory of Complicated Grief (ICG), (2) positive screen on General Health Questionnaire (GHQ), (3) grief intensity (ICG) and (4) psychiatric symptoms (GHQ-12). RESULTS: Among 233 same-gender partners and 329 of different-gender partners, 66.1% [95% confidence interval (CI) 60.0-72.2] and 59.2% [95% CI (53.9-64.6)] respectively screened positive for complicated grief on the ICG, whilst 76.0% [95% CI (70.5-81.5)] and 69.3% [95% CI (64.3-74.3)] respectively screened positive on the GHQ-12. Same-gender bereaved partners were not significantly more likely to screen positive for complicated grief than different-gender partners [adjusted odds ratio (aOR) 1.56, 95% CI (0.98-2.47)], p = 0.059, but same-gender bereaved partners were significantly more likely to screen for psychiatric caseness [aOR 1.67 (1.02, 2.71) p = 0.043]. We similarly found no significant association of partner gender with grief intensity [B = 1.86, 95% CI (-0.91to 4.63), p = 0.188], but significantly greater psychological distress for same-gender partners [B = 1.54, 95% CI (-0.69-2.40), p < 0.001]. CONCLUSIONS: Same-gender bereaved partners report significantly more psychological distress. In view of their poorer sub-clinical mental health, clinical and bereavement services should refine screening processes to identify those at risk of poor mental health outcomes.

LGBT+ partner bereavement and appraisal of the Acceptance-Disclosure Model of LGBT+ bereavement: A qualitative interview study.

BACKGROUND: Support from social networks is vital after the death of a partner. Lesbian, gay, bisexual and/or transgender (LGBT+) people can face disenfranchisement and isolation in bereavement. The Acceptance-Disclosure Model (of LGBT+ bereavement) posits that experiences are shaped by the extent to which individuals feel able to disclose their bereavement to others, and whether that loss is acknowledged appropriately. AIM: To explore LGBT+ specific experiences of partner bereavement; determine decision-making processes regarding disclosure of relationships/identities; and appraise the Acceptance-Disclosure Model using primary qualitative data. DESIGN: Exploratory in-depth qualitative interview study positioned within a social constructivist paradigm. Data were analysed using inductive and deductive reflexive thematic analysis. SETTING/PARTICIPANTS: 21 LGBT+ people from across England bereaved of their civil partner/spouse. RESULTS: Participants described LGBT+ specific stressors in bereavement: lack of recognition of their loss; inappropriate questioning; unwanted disclosure of gender history; and fears of discrimination when accessing support. Disclosure of LGBT+ identities varied across social networks. Some participants described hiding their identities and bereavement to preserve relationships, and challenging intersections between LGBT+ identities and other aspects of culture or self. These findings provide primary evidence to support the Acceptance-Disclosure Model. CONCLUSIONS: LGBT+ people face additional stressors in bereavement. Not all LGBT+ people want to talk directly about their relationships/identities. Sensitive exploration of support needs, aligned with preferences around disclosure of identities, can help foster trust. Five recommendations for inclusive practice are presented. Further research should consider whether the Acceptance-Disclosure Model has utility to explain bereavement experiences for other isolated or disenfranchised groups.

De Novo Designed Peptide and Protein Hairpins Self-Assemble into Sheets and Nanoparticles.

The design and assembly of peptide-based materials has advanced considerably, leading to a variety of fibrous, sheet, and nanoparticle structures. A remaining challenge is to account for and control different possible supramolecular outcomes accessible to the same or similar peptide building blocks. Here a de novo peptide system is presented that forms nanoparticles or sheets depending on the strategic placement of a "disulfide pin" between two elements of secondary structure that drive self-assembly. Specifically, homodimerizing and homotrimerizing de novo coiled-coil α-helices are joined with a flexible linker to generate a series of linear peptides. The helices are pinned back-to-back, constraining them as hairpins by a disulfide bond placed either proximal or distal to the linker. Computational modeling indicates, and advanced microscopy shows, that the proximally pinned hairpins self-assemble into nanoparticles, whereas the distally pinned constructs form sheets. These peptides can be made synthetically or recombinantly to allow both chemical modifications and the introduction of whole protein cargoes as required.

A Contemporary Retrospective Study of Survival in Dogs With Primary Lung Tumors: 40 Cases (2005-2017).

Objective: To report the median survival time in a contemporary cohort of dogs with primary lung tumors and intrathoracic nodal metastasis. Design: Retrospective Case Series. Animals (or sample): Dogs with primary lung tumors treated with lung lobectomy and lymph node biopsy. Procedures: The medical record database at Colorado State University was queried for dogs with primary lung tumors from January 1, 2005 to December 31, 2017. Patients were identified for inclusion if they had lung lobectomy and an intrathoracic lymph node biopsy performed. The median survival time (MST) for lymph node positive (LN+) and negative dogs (LN-) was calculated as well as the MST in dogs that did or did not receive adjuvant chemotherapy. Differences were compared between groups with significance set at p < 0.05. Results: The MST in LN+ dogs (n = 11) was 167 days which was not statistically different from LN- dogs (n = 29) at 456 days (p = 0.2407). No significant difference in the MST in LN+ dogs was identified between dogs that received adjuvant chemotherapy (n = 4; 110 days) and those that did not receive adjuvant chemotherapy (n = 6; 125 days) (p = 0.4409). There was no difference in survival time in LN- dogs receiving chemotherapy (n = 12; 335 days) as compared to those LN- dogs (n = 10) that did not receive adjuvant chemotherapy (258.5 days; p = 0.6475). Conclusions and Clinical Relevance: The survival of primary pulmonary neoplasia in dogs with intrathoracic nodal metastasis is longer than previously reported in this contemporary cohort. Chemotherapy did not appear to improve survival in LN+ or LN- dogs. The combination of tumor size between 100 and 999 cm3 and positive lymph node status significantly reduced survival.

Microbial Degradation of Plastic in Aqueous Solutions Demonstrated by CO2 Evolution and Quantification.

The environmental accumulation of plastics worldwide is a consequence of the durability of the material. Alternative polymers, marketed as biodegradable, present a potential solution to mitigate their ecological damage. However, understanding of biodegradability has been hindered by a lack of reproducible testing methods. We developed a novel method to evaluate the biodegradability of plastic samples based on the monitoring of bacterial respiration in aqueous media via the quantification of CO2 produced, where the only carbon source available is from the polymer. Rhodococcus rhodochrous and Alcanivorax borkumensis were used as model organisms for soil and marine systems, respectively. Our results demonstrate that this approach is reproducible and can be used with a variety of plastics, allowing comparison of the relative biodegradability of the different materials. In the case of low-density polyethylene, the study demonstrated a clear correlation between the molecular weight of the sample and CO2 released, taken as a measure of biodegradability.

Prion protein stabilizes amyloid-ß (Aß) oligomers and enhances Aß neurotoxicity in a Drosophila model of Alzheimer's disease.

The cellular prion protein (PrPC) can act as a cell-surface receptor for ß-amyloid (Aß) peptide; however, a role for PrPC in the pathogenesis of Alzheimer's disease (AD) is contested. Here, we expressed a range of Aß isoforms and PrPC in the Drosophila brain. We found that co-expression of Aß and PrPC significantly reduces the lifespan, disrupts circadian rhythms, and increases Aß deposition in the fly brain. In contrast, under the same conditions, expression of Aß or PrPC individually did not lead to these phenotypic changes. In vitro studies revealed that substoichiometric amounts of PrPC trap Aß as oligomeric assemblies and fragment-preformed Aß fibers. The ability of membrane-anchored PrPC to trap Aß as cytotoxic oligomers at the membrane surface and fragment inert Aß fibers suggests a mechanism by which PrPC exacerbates Aß deposition and pathogenic phenotypes in the fly, supporting a role for PrPC in AD. This study provides a second animal model linking PrPC expression with Aß toxicity and supports a role for PrPC in AD pathogenesis. Blocking the interaction of Aß and PrPC represents a potential therapeutic strategy.

Argonaute Utilization for miRNA Silencing Is Determined by Phosphorylation-Dependent Recruitment of LIM-Domain-Containing Proteins.

As core components of the microRNA-induced silencing complex (miRISC), Argonaute (AGO) proteins interact with TNRC6 proteins, recruiting other effectors of translational repression/mRNA destabilization. Here, we show that LIMD1 coordinates the assembly of an AGO-TNRC6 containing miRISC complex by binding both proteins simultaneously at distinct interfaces. Phosphorylation of AGO2 at Ser 387 by Akt3 induces LIMD1 binding, which in turn enables AGO2 to interact with TNRC6A and downstream effector DDX6. Conservation of this serine in AGO1 and 4 indicates this mechanism may be a fundamental requirement for AGO function and miRISC assembly. Upon CRISPR-Cas9-mediated knockout of LIMD1, AGO2 miRNA-silencing function is lost and miRNA silencing becomes dependent on a complex formed by AGO3 and the LIMD1 family member WTIP. The switch to AGO3 utilization occurs due to the presence of a glutamic acid residue (E390) on the interaction interface, which allows AGO3 to bind to LIMD1, AJUBA, and WTIP irrespective of Akt signaling.

Combined delivery of FGF-2, TGF-ß1, and adipose-derived stem cells from an engineered periosteum to a critical-sized mouse femur defect.

Critical-sized long bone defects suffer from complications including impaired healing and non-union due to substandard healing and integration of devitalized bone allograft. Removal of the periosteum contributes to the limited healing of bone allografts. Restoring a periosteum on bone allografts may provide improved allograft healing and integration. This article reports a polysaccharide-based tissue engineered periosteum that delivers basic fibroblast growth factor (FGF-2), transforming growth factor-ß1 (TGF-ß1), and adipose-derived mesenchymal stem cells (ASCs) to a critical-sized mouse femur defect. The tissue engineered periosteum was evaluated for improving bone allograft healing and incorporation by locally delivering FGF-2, TGF-ß1, and supporting ASCs transplantation. ASCs were successfully delivered and longitudinally tracked at the defect site for at least 7 days post operation with delivered FGF-2 and TGF-ß1 showing a mitogenic effect on the ASCs. At 6 weeks post implantation, data showed a non-significant increase in normalized bone callus volume. However, union ratio analysis showed a significant inhibition in allograft incorporation, confirmed by histological analysis, due to loosening of the nanofiber coating from the allograft surface. Ultimately, this investigation shows our tissue engineered periosteum can deliver FGF-2, TGF-ß1, and ASCs to a mouse critical-sized femur defect and further optimization may yield improved bone allograft healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 900-911, 2017.

Do Mesenchymal Stromal Cells Influence Microscopic Residual or Metastatic Osteosarcoma in a Murine Model?

BACKGROUND: Mesenchymal stromal cells (MSCs) have been shown in rodent models to promote primary and pulmonary metastatic sarcoma growth when injected in the presence of gross tumor. In theory, this would limit their use in a clinical setting after limb salvage treatment for osteosarcoma. Although concerning, these models do not translate to the clinical setting wherein MSCs could be used after primary tumor resection to aid in bone healing and incorporation of tumor endoprostheses. If we can determine whether the use of MSCs in this setting is safe, it might improve our ability to augment bone healing in patients undergoing limb salvage. QUESTIONS/PURPOSES: The purpose of this study was to determine (1) whether MSCs promote pulmonary metastatic disease progression in a murine osteosarcoma model; and/or (2) whether they affect local disease recurrence in the presence of microscopic residual osteosarcoma. METHODS: An orthotopic model of luciferase-expressing osteosarcoma was developed. At 10 days, resection of the primary tumor was performed. One hundred fourteen female C3H mice were inoculated with DLM8-luc osteosarcoma in the proximal tibia. Ninety-four mice developed orthotopic osteosarcoma with luciferase expression. Mice with bioluminescent evidence of a primary tumor received either a microscopically "clean" amputation at a time when residual microscopic metastatic disease was present in the lungs (pulmonary metastasis group; n = 65) or a "dirty" amputation (local recurrence group; n = 29). Mice were randomized to receive intravenous MSCs, MSCs at the surgical site, or no MSCs. Mice were monitored for development and progression of pulmonary metastasis and local recurrence by bioluminescence imaging and daily measurements at the surgical site. The number of pulmonary nodules, time to first evidence of metastasis, and size of recurrent tumor were compared using Kruskal-Wallis, analysis of variance, Welch's, t-tests, or Mann-Whitney tests as appropriate for the specific data sets with p < 0.05 considered significant. RESULTS: Mice receiving intravenous MSCs had a faster time to first detection of pulmonary metastasis (2.93 ± 1.90 days) compared with mice with local injection of MSCs (6.94 ± 6.78 days) or no MSCs (5.93 ± 4.55 days) (p = 0.022). MSC treatment did not influence whether mice developed local recurrence (p = 0.749) or size of recurrent tumors (p = 0.221). CONCLUSIONS: MSCs delivered to the surgical site did not promote local recurrence or size of recurrent tumors, but intravenous injection of MSCs did hasten onset of detection of pulmonary metastatic disease. Although local administration of MSCs into a surgical site does not appear to promote either pulmonary metastatic disease or local recurrence, large variation within groups and small numbers diminished statistical power such that a Type II error cannot be ruled out. CLINICAL RELEVANCE: If MSCs are to be used to augment bone healing in the postlimb salvage setting in patients with osteosarcoma, it will be important to understand their influence, if any, on pulmonary micrometastsis or residual microscopic local disease. Although murine models do not completely recapitulate the clinical scenario, these results suggest that intravenous delivery of MSCs may promote micrometastatic pulmonary disease. Local administration into a surgical wound, even in the presence of residual microscopic disease, may be safe, at least in this murine model, but further investigation is warranted before considering the use of MSCs for clinical use in patients with osteosarcoma.

SUMOylation regulates the homologous to E6-AP carboxyl terminus (HECT) ubiquitin ligase Rsp5p.

The post-translational modifiers ubiquitin and small ubiquitin-related modifier (SUMO) regulate numerous critical signaling pathways and are key to controlling the cellular fate of proteins in eukaryotes. The attachment of ubiquitin and SUMO involves distinct, but related, machinery. However, it is now apparent that many substrates can be modified by both ubiquitin and SUMO and that some regulatory interaction takes place between the respective attachment machinery. Here, we demonstrate that the Saccharomyces cerevisiae ubiquitin ligase Rsp5p, a member of the highly conserved Nedd4 family of ubiquitin ligases, is SUMOylated in vivo. We further show that Rsp5p SUMOylation is mediated by the SUMO ligases Siz1p and Siz2p, members of the conserved family of PIAS SUMO ligases that are, in turn, substrates for Rsp5p-mediated ubiquitylation. Our experiments show that SUMOylated Rsp5p has reduced ubiquitin ligase activity, and similarly, ubiquitylated Siz1p demonstrates reduced SUMO ligase activity leading to respective changes in both ubiquitin-mediated sorting of the manganese transporter Smf1p and polySUMO chain formation. This reciprocal regulation of these highly conserved ligases represents an exciting and previously unidentified system of cross talk between the ubiquitin and SUMO systems.

Elucidation of the biosynthesis of the di-C-glycosylflavone isoschaftoside, an allelopathic component from Desmodium spp. that inhibits Striga spp. development.

Isoschaftoside, an allelopathic di-C-glycosylflavone from Desmodium spp. root exudates, is biosynthesised through sequential glucosylation and arabinosylation of 2-hydroxynaringenin with UDP-glucose and UDP-arabinose. Complete conversion to the flavone requires chemical dehydration implying a dehydratase enzyme has a role in vivo to complete the biosynthesis. The C-glucosyltransferase has been partially characterised and its activity demonstrated in highly purified fractions.

Pseudomonas aeruginosa possesses two putative type I signal peptidases, LepB and PA1303, each with distinct roles in physiology and virulence.

Type I signal peptidases (SPases) cleave signal peptides from proteins during translocation across biological membranes and hence play a vital role in cellular physiology. SPase activity is also of fundamental importance to the pathogenesis of infection for many bacteria, including Pseudomonas aeruginosa, which utilizes a variety of secreted virulence factors, such as proteases and toxins. P. aeruginosa possesses two noncontiguous SPase homologues, LepB (PA0768) and PA1303, which share 43% amino acid identity. Reverse transcription (RT)-PCR showed that both proteases were expressed, while a FRET-based assay using a peptide based on the signal sequence cleavage region of the secreted LasB elastase showed that recombinant LepB and PA1303 enzymes were both active. LepB is positioned within a genetic locus that resembles the locus containing the extensively characterized SPase of E. coli and is of similar size and topology. It was also shown to be essential for viability and to have high sequence identity with SPases from other pseudomonads (≥ 78%). In contrast, PA1303, which is small for a Gram-negative SPase (20 kDa), was found to be dispensable. Mutation of PA1303 resulted in an altered protein secretion profile and increased N-butanoyl homoserine lactone production and influenced several quorum-sensing-controlled phenotypic traits, including swarming motility and the production of rhamnolipid and elastinolytic activity. The data indicate different cellular roles for these P. aeruginosa SPase paralogues; the role of PA1303 is integrated with the quorum-sensing cascade and includes the suppression of virulence factor secretion and virulence-associated phenotypes, while LepB is the primary SPase.

Bul proteins, a nonredundant, antagonistic family of ubiquitin ligase regulatory proteins.

Like other Nedd4 ligases, Saccharomyces cerevisiae E3 Rsp5p utilizes adaptor proteins to interact with some substrates. Previous studies have indentified Bul1p and Bul2p as adaptor proteins that facilitate the ligase-substrate interaction. Here, we show the identification of a third member of the Bul family, Bul3p, the product of two adjacent open reading frames separated by a stop codon that undergoes readthrough translation. Combinatorial analysis of BUL gene deletions reveals that they regulate some, but not all, of the cellular pathways known to involve Rsp5p. Surprisingly, we find that Bul proteins can act antagonistically to regulate the same ubiquitin-dependent process, and the nature of this antagonistic activity varies between different substrates. We further show, using in vitro ubiquitination assays, that the Bul proteins have different specificities for WW domains and that the two forms of Bul3p interact differently with Rsp5p, potentially leading to alternate functional outcomes. These data introduce a new level of complexity into the regulatory interactions that take place between Rsp5p and its adaptors and substrates and suggest a more critical role for the Bul family of proteins in controlling adaptor-mediated ubiquitination.

Neurite-like structures induced by mevalonate pathway blockade are due to the stability of cell adhesion foci and are enhanced by the presence of APP.

Epidemiological studies have shown an association between statin use and a decreased risk of dementia. However, the mechanism by which this beneficial effect is brought about is unclear. In the context of Alzheimer's disease, at least three possibilities have been studied; reduction in amyloid beta peptide (Abeta) production, the promotion of alpha-secretase cleavage and positive effects on neurite outgrowth. By investigating the effects of mevalonate pathway blockade on neurite outgrowth using real-time imaging, we found that rather than promote the production of neurite extensions, inhibition rapidly induced cell rounding. Crucially, neurite-like structures were generated through the persistence of cell-cell and cell-substrate adhesions and not through a mechanism of positive outgrowth. This effect can be strikingly enhanced by the over-expression of human amyloid precursor protein and is isoprenoid rather than cholesterol dependent.

Demonstration that CobG, the monooxygenase associated with the ring contraction process of the aerobic cobalamin (vitamin B12) biosynthetic pathway, contains an Fe-S center and a mononuclear non-heme iron center.

The ring contraction process that occurs during cobalamin (vitamin B(12)) biosynthesis is mediated via the action of two enzymes, CobG and CobJ. The first of these generates a tertiary alcohol at the C-20 position of precorrin-3A by functioning as a monooxygenase, a reaction that also forms a gamma lactone with the acetic acid side chain on ring A. The product, precorrin-3B, is then acted upon by CobJ, which methylates at the C-17 position and promotes ring contraction of the macrocycle by catalyzing a masked pinacol rearrangement. Here, we report the characterization of CobG enzymes from Pseudomonas denitrificans and Brucella melitensis. We show that both contain a [4Fe-4S] center as well as a mononuclear non-heme iron. Although both enzymes are active in vivo, the P. denitrificans enzyme was found to be inactive in vitro. Further analysis of this enzyme revealed that the mononuclear non-heme iron was not reducible, and it was concluded that it is rapidly inactivated once it is released from the bacterial cell. In contrast, the B. melitensis enzyme was found to be fully active in vitro and the mononuclear non-heme iron was reducible by dithionite. The reduced mononuclear non-heme was able to react with the oxygen analogue NO, but only in the presence of the substrate precorrin-3A. The cysteine residues responsible for binding the Fe-S center were identified by site-directed mutagenesis. A mechanism for CobG is presented.