pH-Tolerant Wet Adhesion of Catechol Analogs.

The need for improved wet adhesives has driven research on mussel-inspired materials incorporating dihydroxyphenylalanine (DOPA) and related analogs of the parent catechol, but their susceptibility to oxidation limits practical application of these functionalities. Here, we investigate the molecular-level adhesion of the catechol analogs dihydroxybenzamide (DHB) and hydroxypyridinone (HOPO) as a function of pH. We find that the molecular structure of the catechol analogs influences their susceptibility to oxidation in alkaline conditions, with HOPO emerging as a particularly promising candidate for pH-tolerant adhesives for diverse environmental conditions.

Tistrellabactins A and B Are Photoreactive C-Diazeniumdiolate Siderophores from the Marine-Derived Strain Tistrella mobilis KA081020-065.

The C-diazeniumdiolate group in the amino acid graminine is emerging as a new microbially produced Fe(III) coordinating ligand in siderophores, which is photoreactive. While the few siderophores reported from this class have only been isolated from soil-associated microbes, here we report the first C-diazeniumdiolate siderophores tistrellabactins A and B, isolated from the bioactive marine-derived strain Tistrella mobilis KA081020-065. The structural characterization of the tistrellabactins reveals unique biosynthetic features including an NRPS module iteratively loading glutamine residues and a promiscuous adenylation domain yielding either tistrellabactin A with an asparagine residue or tistrellabactin B with an aspartic acid residue at analogous positions. Beyond the function of scavenging Fe(III) for growth, these siderophores are photoreactive upon irradiation with UV light, releasing the equivalent of nitric oxide (NO) and an H atom from the C-diazeniumdiolate group. Fe(III)-tistrellabactin is also photoreactive, with both the C-diazeniumdiolate and the ß-hydroxyaspartate residues undergoing photoreactions, resulting in a photoproduct without the ability to chelate Fe(III).

The impact of donor consent mechanism on organ procurement organization performance in the United States.

BACKGROUND: Lack of donor organ availability represents a major limitation to the success of solid organ transplantation. The Scientific Registry of Transplant Recipients (SRTR) publishes performance reports of organ procurement organizations (OPO) in the United States, but does not stratify by the mechanism of donor consent, namely first-person authorization (organ donor registry) and next-of-kin authorization. This study aimed to report the trends in deceased organ donation in the United States and assess the regional differences in OPO performance after accounting for the different mechanisms of donor consent. METHODS: The SRTR database was queried for all eligible deaths (2008-2019) which were then stratified based on the mechanism of donor authorization. Multivariable logistic regression was performed to assess the probability of organ donation across OPOs based on specific donor consent mechanisms. Eligible deaths were divided into 3 cohorts based on the probability to donate. Consent rates at the OPO level were calculated for each cohort. RESULTS: Organ donor registration among adult eligible deaths in the U.S. increased over time (2008: 10% vs 2019: 39%, p < 0.001), coincident with a decline in next-of-kin authorization rates (2008: 70% vs 2019: 64%, p < 0.001). At the OPO level, the increased organ donor registration was associated with lower next-of-kin authorization rates. Among eligible deaths with medium- and low-probability of donation, recruitment was highly variable across OPO's, ranging from 36% to 75% in the medium-probability group (median 54%, IQR 50%-59%) and 8% and 73% in the low-probability group (median 30%, IQR 17%-38%). CONCLUSION: Significant variability exists across OPOs in the consent of potentially persuadable donors after adjusting for population demographic differences and the mechanism of consent. Current metrics may not truly reflect OPO performance as they do not account for consent mechanism. There is further opportunity for improvement in deceased organ donation through targeted initiatives across OPOs, modeled after regions with the best performance.

Perceptions of pediatric deceased donor consent: A survey of organ procurement organizations.

BACKGROUND: Children awaiting transplantation face a high risk of waitlist mortality due to a shortage of pediatric organ donors. Pediatric donation consent rates vary across Organ Procurement Organizations (OPOs), suggesting that some OPOs might utilize more effective pediatric-focused donor recruitment techniques than others. An online survey of 193 donation requestor staff sheds light on the strategies that OPO staff utilize when approaching potential pediatric deceased organ donors. METHODS: In collaboration with the Association of Organ Procurement Organizations, the research team contacted the executive directors and medical directors of all 57 of the OPOs in the US. Of these, 51 OPOs agreed to participate, and 47 provided contact information for donation requestor staff. Of the 379 staff invited to participate in the survey, 193 provided complete responses. RESULTS: Respondents indicated more comfort approaching adult donors than pediatric donors, and they endorsed approach techniques that were interpersonal and emotional rather than professional and informative. Respondents were accurate in their perceptions about which donor characteristics are associated with consent. However, respondents from OPOs with high consent rates (according to data from the Scientific Registry of Transplant Recipients), and those from OPOs with low consent rates were very similar in terms of demographics, training, experience, and reported techniques. CONCLUSIONS: Additional research is needed to better determine why some OPOs have higher consent rates than others and whether the factors that lead to high consent rates in high-performing OPOs can be successful when implemented by lower-performing OPOs.

Mining elements of siderophore chirality encoded in microbial genomes.

The vast majority of bacteria require iron to grow. A significant iron acquisition strategy is the production of siderophores, which are secondary microbial metabolites synthesized to sequester iron(III). Siderophore structures encompass a variety of forms, of which highly modified peptidic siderophores are of interest herein. State-of-the-art genome mining tools, such as antiSMASH (antibiotics & Secondary Metabolite Analysis SHell), hold the potential to predict and discover new peptidic siderophores, including a combinatoric suite of triscatechol siderophores framed on a triserine-ester backbone of the general class, (DHB-l/d CAA-l Ser)3 (CAA, cationic amino acid). Siderophores with l/d Arg, l/d Lys and l Orn, but not d Orn, were predicted in bacterial genomes. Fortuitously the d Orn siderophore was identified, yet its lack of prediction highlights the limitation of current genome mining tools. The full combinatoric suite of these siderophores, which form chiral iron(III) complexes, reveals stereospecific coordination chemistry encoded in microbial genomes. The chirality embedded in this suite of Fe(III)-siderophores raises the question of whether the relevant siderophore-mediated iron acquisition pathways are stereospecific and selective for ferric siderophore complexes of a defined configuration.

C-Diazeniumdiolate Graminine in the Siderophore Gramibactin Is Photoreactive and Originates from Arginine.

Siderophores are synthesized by microbes to facilitate iron acquisition required for growth. Catecholate, hydroxamate, and α-hydroxycarboxylate groups comprise well-established ligands coordinating Fe(III) in siderophores. Recently, a C-type diazeniumdiolate ligand in the newly identified amino acid graminine (Gra) was found in the siderophore gramibactin (Gbt) produced by Paraburkholderia graminis DSM 17151. The N-N bond in the diazeniumdiolate is a distinguishing feature of Gra, yet the origin and reactivity of this C-type diazeniumdiolate group has remained elusive until now. Here, we identify l-arginine as the direct precursor to l-Gra through the isotopic labeling of l-Arg, l-ornithine, and l-citrulline. Furthermore, these isotopic labeling studies establish that the N-N bond in Gra must be formed between the Nδ and Nω of the guanidinium group in l-Arg. We also show the diazeniumdiolate groups in apo-Gbt are photoreactive, with loss of nitric oxide (NO) and H+ from each d-Gra yielding E/Z oxime isomers in the photoproduct. With the loss of Gbt's ability to chelate Fe(III) upon exposure to UV light, our results hint at this siderophore playing a larger ecological role. Not only are NO and oximes important in plant biology for communication and defense, but so too are NO-releasing compounds and oximes attractive in medicinal applications.

On the origin of amphi-enterobactin fragments produced by Vibrio campbellii species.

Amphi-enterobactin is an amphiphilic siderophore isolated from a variety of microbial Vibrio species. Like enterobactin, amphi-enterobactin is a triscatecholate siderophore; however, it is framed on an expanded tetralactone core comprised of four L-Ser residues, of which one L-Ser is appended by a fatty acid and the remaining L-Ser residues are appended by 2,3-dihydroxybenzoate (DHB). Fragments of amphi-enterobactin composed of 2-Ser-1-DHB-FA and 3-Ser-2-DHB-FA have been identified in the supernatant of Vibrio campbellii species. The origin of these fragments has not been determined, although two distinct isomers could exist for 2-Ser-1-DHB-FA and three distinct isomers could exist for 3-Ser-2-DHB-FA. The fragments of amphi-enterobactin could originate from hydrolysis of the amphi-enterobactin macrolactone, or from premature release due to an inefficient biosynthetic pathway. Unique masses in the tandem MS analysis establish that certain fragments isolated from the culture supernatant must originate from hydrolysis of the amphi-enterobactin macrolactone, while others cannot be distinguished from premature release during biosynthesis or hydrolysis of amphi-enterobactin.

Don't Throw Your Heart Away: Increased Transparency of Donor Utilization Practices in Transplant Center Report Cards Alters How Center Performance Is Evaluated.

BACKGROUND: Publicly available report cards for transplant centers emphasize posttransplant survival and obscure the fact that some centers reject many of the donor organs they are offered (reflecting a conservative donor acceptance strategy), while others accept a broader range of donor offers (reflecting an open donor acceptance strategy). OBJECTIVE: We assessed how the provision of salient information about donor acceptance practices and waitlist survival rates affected evaluation judgments of hospital report cards given by laypeople and medical trainees. METHODS: We tested 5 different report card formats across 4 online randomized experiments (n1 = 1,003, n2 = 105, n3 = 123, n4 = 807) in the same hypothetical decision. The primary outcome variable was a binary choice between transplant hospitals (one with an open donor acceptance strategy and the other with a conservative donor acceptance strategy). RESULTS: Report cards featuring salient information about donor organ utilization rates (transplant outcomes categorized by quality of donor offers accepted) or overall survival rates (outcomes from both waitlist and transplanted patients) led lay participants (studies 1, 3, and 4) and medical trainees (study 2) to evaluate transplant centers with open donor acceptance strategies more favorably than centers with conservative strategies. LIMITATIONS: Due to the nature of the decision, a hypothetical scenario was necessary for both ethical and practical reasons. Results may not generalize to transplant clinicians or patients faced with the decision of where to join the transplant waitlist. CONCLUSIONS: These findings suggest that performance evaluations for transplant centers may vary significantly based not only on what outcome information is presented in report cards but also how the information is displayed.

Ruckerbactin Produced by Yersinia ruckeri YRB Is a Diastereomer of the Siderophore Trivanchrobactin Produced by Vibrio campbellii DS40M4.

The Gram-negative bacterium Yersinia ruckeri is the causative agent for enteric red mouth disease in salmonids. The genome of Y. ruckeri YRB contains a biosynthetic gene cluster encoding the biosynthesis of catechol siderophores that are diastereomeric with the known vanchrobactin class of siderophores, (DHBDArgLSer)(1-3). Ruckerbactin (1), produced by Y. ruckeri YRB, was found to be the linear tris-l-serine ester composed of l-arginine and 2,3-dihydroxybenzoic acid, (DHBLArgLSer)3. The biscatechol, (DHBLArgLSer)2 (2), and monocatechol, DHBLArgLSer (3), compounds were also isolated and characterized. The macrolactone of ruckerbactin was not detected. The presence of LArg in ruckerbactin makes it the diastereomer of trivanchrobactin with DArg. The electronic circular dichroism spectra of Fe(III)-ruckerbactin and Fe(III)-trivanchrobactin reveal the opposite enantiomeric configurations at the Fe(III) sites. Fe(III)-ruckerbactin adopts the Δ configuration, and Fe(III)-trivanchrobactin adopts the Λ configuration. Y. ruckeri YRB was also found to produce the antimicrobial agent holomycin (4).

Genomics-driven discovery of chiral triscatechol siderophores with enantiomeric Fe(iii) coordination.

Ferric complexes of triscatechol siderophores may assume one of two enantiomeric configurations at the iron site. Chirality is known to be important in the iron uptake process, however an understanding of the molecular features directing stereospecific coordination remains ambiguous. Synthesis of the full suite of (DHBL/DLysL/DSer)3 macrolactone diastereomers, which includes the siderophore cyclic trichrysobactin (CTC), enables the effects that the chirality of Lys and Ser residues exert on the configuration of the Fe(iii) complex to be defined. Computationally optimized geometries indicate that the Λ/Δ configurational preferences are set by steric interactions between the Lys sidechains and the peptide backbone. The ability of each (DHBL/DLysL/DSer)3 diastereomer to form a stable Fe(iii) complex prompted a genomic search for biosynthetic gene clusters (BGCs) encoding the synthesis of these diastereomers in microbes. The genome of the plant pathogen Dickeya chrysanthemi EC16 was sequenced and the genes responsible for the biosynthesis of CTC were identified. A related but distinct BGC was identified in the genome of the opportunistic pathogen Yersinia frederiksenii ATCC 33641; isolation of the siderophore from Y. frederiksenii ATCC 33641, named frederiksenibactin (FSB), revealed the triscatechol oligoester, linear-(DHBLLysLSer)3. Circular dichroism (CD) spectroscopy establishes that Fe(iii)-CTC and Fe(iii)-FSB are formed in opposite enantiomeric configuration, consistent with the results of the ferric complexes of the cyclic (DHBL/DLysL/DSer)3 diastereomers.

Predictors of Deceased Organ Donation in the Pediatric Population.

BACKGROUND: A shortage of donor organs represents the major barrier to the success of solid organ transplantation. This is especially true in the pediatric population for which the number of organ donors has decreased over time. With this study, we aimed to assess the factors associated with deceased organ donor consent in the pediatric population and determine the variability in consent rates across organ procurement organizations (OPOs). METHODS: All eligible pediatric deaths were identified from the Scientific Registry of Transplant Recipients (2008-2019). The rate of organ donor consent was determined, and multivariable logistic regression was used to assess the factors independently associated with successful donor recruitment. The probability of donor consent was determined for each OPO after adjusting for patient demographics. RESULTS: A total of 11 829 eligible pediatric deaths were approached to request consent for organ donation. Consent was successful in 8816 (74.5%) subjects. Consent rates are lower in the pediatric population compared with young adults and are directly related to patient age such that eligible infant deaths have the lowest rate of successful donor consent. There is significant variability in donor consent rates across OPOs, independent of population demographic differences. CONCLUSIONS: OPO is predictive of pediatric deceased organ donor consent independent of demographic differences, with some regions having consistently higher consent rates than others. Sharing best practices for pediatric deceased donor recruitment may be a strategy to increase organ availability in the pediatric population.

Photoactive siderophores: Structure, function and biology.

It is well known that bacteria and fungi have evolved sophisticated systems for acquiring the abundant but biologically inaccessible trace element iron. These systems are based on high affinity Fe(III)-specific binding compounds called siderophores which function to acquire, transport, and process this essential metal ion. Many hundreds of siderophores are now known and their numbers continue to grow. Extensive studies of their isolation, structure, transport, and molecular genetics have been undertaken in the last three decades and have been comprehensively reviewed many times. In this review we focus on a unique subset of siderophores that has only been recognized in the last 20 years, namely those whose iron complexes display photoactivity. This photoactivity, which typically results in the photooxidation of the siderophore ligand with concomitant reduction of Fe(III) to Fe(II), seemingly upsets the siderophore paradigm of forming and transporting only extremely stable Fe(III) complexes into microbial cells. Here we review their structure, synthesis, photochemistry, photoproduct coordination chemistry and explore the potential biological and ecological consequences of this photoactivity.

Precursor-directed biosynthesis of catechol compounds in Acinetobacter bouvetii DSM 14964.

Genome mining for VibH homologs reveals several species of Acinetobacter with a gene cluster that putatively encodes the biosynthesis of catechol siderophores with an amine core. A. bouvetii DSM 14964 produces three novel biscatechol siderophores: propanochelin (1), butanochelin (2), and pentanochelin (3). This strain has a relaxed specificity for the amine substrate, allowing for the biosynthesis of a variety of non-natural siderophore analogs by precursor directed biosynthesis. Of potential synthetic utility, A. bouvetii DSM 14964 condenses 2,3-dihydroxybenzoic acid (2,3-DHB) to allylamine and propargylamine, producing catecholic compounds which bind iron(iii) and may be further modified via thiol-ene or azide-alkyne click chemistry.

ISHLT consensus statement on donor organ acceptability and management in pediatric heart transplantation.

The number of potential pediatric heart transplant recipients continues to exceed the number of donors, and consequently the waitlist mortality remains significant. Despite this, around 40% of all donated organs are not used and are discarded. This document (62 authors from 53 institutions in 17 countries) evaluates factors responsible for discarding donor hearts and makes recommendations regarding donor heart acceptance. The aim of this statement is to ensure that no usable donor heart is discarded, waitlist mortality is reduced, and post-transplant survival is not adversely impacted.

Behavioral economics-A framework for donor organ decision-making in pediatric heart transplantation.

The high discard rate of pediatric donor hearts presents a major challenge for children awaiting heart transplantation. Recent literature identifies several factors that contribute to the disparities in pediatric donor heart usage, including regulatory oversight, the absence of guidelines on pediatric donor heart acceptance, and variation among transplant programs. However, a likely additional contributor to this issue are the behavioral factors influencing transplant team decisions in donor offer scenarios, a topic that has not yet been studied in detail. Behavioral economics and decision psychology provide an excellent foundation for investigating decision-making in the pediatric transplant setting, offering key insights into the behavior of transplant professionals. We conducted a systematic review of published literature in pediatric heart transplant related to behavioral economics and the psychology of decision-making. In this review, we draw on paradigms from these two domains in order to examine how existing aspects of the transplant environment, including regulatory oversight, programmatic variation, and allocation systems, may precipitate potential biases surrounding donor offer decisions. Recognizing how human decision behavior influences donor acceptance is a first step toward improving utilization of potentially viable pediatric donor hearts.

Patients and their family members prioritize post-transplant survival over waitlist survival when considering donor hearts for transplantation.

Heart transplant providers often focus on post-transplant outcomes when making donor decisions, potentially at the expense of higher waitlist mortality. This study aimed to assess public opinion regarding the selection of donor hearts and the balance between pre- and post-transplant risk. The authors generated a survey to investigate public opinion regarding donor acceptance. The survey was shared freely online across social media platforms in April-May 2019. A total of 718 individuals responded to the survey, with an equal distribution between patients and family members. Respondents consistently favored post-transplant outcomes over waitlist outcomes. About 83.9% of respondents favored a hospital with longer waitlist times, worse waitlist outcomes, but excellent post-transplant survival over a hospital with short waitlist times, a high waitlist survival, and inferior post-transplant survival. This preference was no different between pediatric and adult populations (P = .7), patient and family members (P = .935), or those with a pre- vs post-transplant perspective (P = .985). Patients and their family members consistently favor improved post-transplant survival over waitlist survival when considering the risks of accepting a donor organ. These findings suggest that current practice patterns of donor selection align with the opinions of patients and family members with heart failure or who have undergone heart transplantation.

Impact of Molecular Architecture and Adsorption Density on Adhesion of Mussel-Inspired Surface Primers with Catechol-Cation Synergy.

Marine mussels secrete proteins rich in residues containing catechols and cationic amines that displace hydration layers and adhere to charged surfaces under water via a cooperative binding effect known as catechol-cation synergy. Mussel-inspired adhesives containing paired catechol and cationic functionalities are a promising class of materials for biomedical applications, but few studies address the molecular adhesion mechanism(s) of these materials. To determine whether intramolecular adjacency of these functionalities is necessary for robust adhesion, a suite of siderophore analog surface primers was synthesized with systematic variations in intramolecular spacing between catechol and cationic functionalities. Adhesion measurements conducted with a surface forces apparatus (SFA) allow adhesive failure to be distinguished from cohesive failure and show that the failure mode depends critically on the siderophore analog adsorption density. The adhesion of these molecules to muscovite mica in an aqueous electrolyte solution demonstrates that direct intramolecular adjacency of catechol and cationic functionalities is not necessary for synergistic binding. However, we show that increasing the catechol-cation spacing by incorporating nonbinding domains results in decreased adhesion, which we attribute to a decrease in the density of catechol functionalities. A mechanism for catechol-cation synergy is proposed based on electrostatically driven adsorption and subsequent binding of catechol functionalities. This work should guide the design of new adhesives for binding to charged surfaces in saline environments.

Genomic analysis of siderophore ß-hydroxylases reveals divergent stereocontrol and expands the condensation domain family.

Genome mining of biosynthetic pathways streamlines discovery of secondary metabolites but can leave ambiguities in the predicted structures, which must be rectified experimentally. Through coupling the reactivity predicted by biosynthetic gene clusters with verified structures, the origin of the ß-hydroxyaspartic acid diastereomers in siderophores is reported herein. Two functional subtypes of nonheme Fe(II)/α-ketoglutarate-dependent aspartyl ß-hydroxylases are identified in siderophore biosynthetic gene clusters, which differ in genomic organization-existing either as fused domains (IßHAsp) at the carboxyl terminus of a nonribosomal peptide synthetase (NRPS) or as stand-alone enzymes (TßHAsp)-and each directs opposite stereoselectivity of Asp ß-hydroxylation. The predictive power of this subtype delineation is confirmed by the stereochemical characterization of ß-OHAsp residues in pyoverdine GB-1, delftibactin, histicorrugatin, and cupriachelin. The l-threo (2S, 3S) ß-OHAsp residues of alterobactin arise from hydroxylation by the ß-hydroxylase domain integrated into NRPS AltH, while l-erythro (2S, 3R) ß-OHAsp in delftibactin arises from the stand-alone ß-hydroxylase DelD. Cupriachelin contains both l-threo and l-erythro ß-OHAsp, consistent with the presence of both types of ß-hydroxylases in the biosynthetic gene cluster. A third subtype of nonheme Fe(II)/α-ketoglutarate-dependent enzymes (IßHHis) hydroxylates histidyl residues with l-threo stereospecificity. A previously undescribed, noncanonical member of the NRPS condensation domain superfamily is identified, named the interface domain, which is proposed to position the ß-hydroxylase and the NRPS-bound amino acid prior to hydroxylation. Through mapping characterized ß-OHAsp diastereomers to the phylogenetic tree of siderophore ß-hydroxylases, methods to predict ß-OHAsp stereochemistry in silico are realized.