A simple mechanism for integration of quorum sensing and cAMP signalling in Vibrio cholerae.

Many bacteria use quorum sensing to control changes in lifestyle. The process is regulated by microbially derived 'autoinducer' signalling molecules, that accumulate in the local environment. Individual cells sense autoinducer abundance, to infer population density, and alter their behaviour accordingly. In Vibrio cholerae, quorum-sensing signals are transduced by phosphorelay to the transcription factor LuxO. Unphosphorylated LuxO permits expression of HapR, which alters global gene expression patterns. In this work, we have mapped the genome-wide distribution of LuxO and HapR in V. cholerae. Whilst LuxO has a small regulon, HapR targets 32 loci. Many HapR targets coincide with sites for the cAMP receptor protein (CRP) that regulates the transcriptional response to carbon starvation. This overlap, also evident in other Vibrio species, results from similarities in the DNA sequence bound by each factor. At shared sites, HapR and CRP simultaneously contact the double helix and binding is stabilised by direct interaction of the two factors. Importantly, this involves a CRP surface that usually contacts RNA polymerase to stimulate transcription. As a result, HapR can block transcription activation by CRP. Thus, by interacting at shared sites, HapR and CRP integrate information from quorum sensing and cAMP signalling to control gene expression. This likely allows V. cholerae to regulate subsets of genes during the transition between aquatic environments and the human host.

A simple mechanism for integration of quorum sensing and cAMP signalling in V. cholerae.

Many bacteria use quorum sensing to control changes in lifestyle. The process is regulated by microbially derived "autoinducer" signalling molecules, that accumulate in the local environment. Individual cells sense autoinducer abundance, to infer population density, and alter their behaviour accordingly. In Vibrio cholerae , quorum sensing signals are transduced by phosphorelay to the transcription factor LuxO. Unphosphorylated LuxO permits expression of HapR, which alters global gene expression patterns. In this work, we have mapped the genome-wide distribution of LuxO and HapR in V. cholerae . Whilst LuxO has a small regulon, HapR targets 32 loci. Many HapR targets coincide with sites for the cAMP receptor protein (CRP) that regulates the transcriptional response to carbon starvation. This overlap, also evident in other Vibrio species, results from similarities in the DNA sequence bound by each factor. At shared sites, HapR and CRP simultaneously contact the double helix and binding is stabilised by direct interaction of the two factors. Importantly, this involves a CRP surface that usually contacts RNA polymerase to stimulate transcription. As a result, HapR can block transcription activation by CRP. Thus, by interacting at shared sites, HapR and CRP integrate information from quorum sensing and cAMP signalling to control gene expression. This likely allows V. cholerae to regulate subsets of genes during the transition between aquatic environments and the human host.

An entropic safety catch controls hepatitis C virus entry and antibody resistance.

E1 and E2 (E1E2), the fusion proteins of Hepatitis C Virus (HCV), are unlike that of any other virus yet described, and the detailed molecular mechanisms of HCV entry/fusion remain unknown. Hypervariable region-1 (HVR-1) of E2 is a putative intrinsically disordered protein tail. Here, we demonstrate that HVR-1 has an autoinhibitory function that suppresses the activity of E1E2 on free virions; this is dependent on its conformational entropy. Thus, HVR-1 is akin to a safety catch that prevents premature triggering of E1E2 activity. Crucially, this mechanism is turned off by host receptor interactions at the cell surface to allow entry. Mutations that reduce conformational entropy in HVR-1, or genetic deletion of HVR-1, turn off the safety catch to generate hyper-reactive HCV that exhibits enhanced virus entry but is thermally unstable and acutely sensitive to neutralising antibodies. Therefore, the HVR-1 safety catch controls the efficiency of virus entry and maintains resistance to neutralising antibodies. This discovery provides an explanation for the ability of HCV to persist in the face of continual immune assault and represents a novel regulatory mechanism that is likely to be found in other viral fusion machinery.

Ensuring a Locally Tailored Response to Early Onset Sepsis Screening Meets or Exceeds the Performance of Published Approaches.

BACKGROUND: Evaluation of well-appearing neonates for early-onset sepsis (EOS) remains controversial. Multiple risk stratification approaches are currently used for the evaluation of EOS. Our aim was to quantify and compare frequency of laboratory evaluation and empirical antibiotics between published and local EOS approaches. METHODS: This retrospective cohort study included 8240 infants born ≥35 + 0/7 weeks' gestation at an institution from October 1, 2014, to March 1, 2018. Excluded from analysis were 156 patients who exhibited either major congenital anomalies or required antibiotics for surgical issues. A total of 1680 patient charts with risk factors for EOS were reviewed for further demographic data, clinical presentation, laboratory results, and probable recommendations from 4 EOS risk assessment approaches. RESULTS: Laboratory evaluation recommendation was 7.1% for Centers for Disease Control and Prevention 2010 guidelines and local 2016 EOS algorithm, 6% for local 2019 EOS algorithm, and 5.9% for Kaiser Permanente neonatal EOS calculator (neonatal EOS calculator). Antibiotic recommendation was 6% for 2010 Centers for Disease Control and Prevention guidelines, 4.3% for neonatal EOS calculator, and 3.3% for local 2016 and 2019 EOS algorithms. CONCLUSIONS: Of the 4 approaches reviewed, the local 2019 EOS algorithm and the neonatal EOS calculator were similar in recommending the lowest frequency of laboratory evaluation and the local 2016 and 2019 EOS algorithms had the lowest recommended antibiotic usage in this population.

Evaluation of Intraoperative, Local Site Injections of Liposomal Bupivacaine as an Alternative to Standard Local Anesthetics in Patients Undergoing Total Hip Arthroplasty.

Background: Achieving postsurgical pain control after total hip arthroplasty (THA) is a critical factor for successful recovery because inadequately treated pain may lead to a delay in ambulation and hospital discharge and have an adverse impact on a patient's quality of life. Objective: This study compares the effectiveness of immediate-release local anesthetics for pain control in THA vs liposomal bupivacaine (LB) related to patient outcomes and costs of care. Methods: This is a retrospective cohort study of consecutive patients undergoing THA at 3 hospitals from January 2013 to July 2016. The control group received plain bupivacaine or ropivacaine while the study group received LB. Generalized linear models were used controlling for several patient factors. Primary measures included length of stay (LOS), hospitalization costs, pain relief, opioid use, and mobility. Secondary outcomes were discharge disposition and 30-, 60-, and 90-day readmissions. Results: One hundred and ninety-six patients were identified, with 103 as controls, 70 receiving LB, and 23 excluded. The LB group showed a decrease in LOS of 0.5 days (2.5 ± 2.6 vs 3.0 ± 2.1 days, P = .010), increased mobility on the day of surgery (27.6 ± 49.3 vs 12.5 ± 48.5 feet, P = .001) and the first day after surgery (186.8 ± 133.8 vs 155.2 ± 135.6, P = .039), and decreased hospital costs ($10 670 vs $11 351, P = .022). There were no significant differences in pain scores, opioid use, adverse events, discharge disposition, or readmissions. Study limitations include retrospective analysis, unblinded participants, and generalizability of results. Conclusions: LB provides an effective alternative to standard local anesthetics in patients undergoing THA based on improvements of inpatient parameters, LOS, and cost measures.

The quorum sensing transcription factor AphA directly regulates natural competence in Vibrio cholerae.

Many bacteria use population density to control gene expression via quorum sensing. In Vibrio cholerae, quorum sensing coordinates virulence, biofilm formation, and DNA uptake by natural competence. The transcription factors AphA and HapR, expressed at low and high cell density respectively, play a key role. In particular, AphA triggers the entire virulence cascade upon host colonisation. In this work we have mapped genome-wide DNA binding by AphA. We show that AphA is versatile, exhibiting distinct modes of DNA binding and promoter regulation. Unexpectedly, whilst HapR is known to induce natural competence, we demonstrate that AphA also intervenes. Most notably, AphA is a direct repressor of tfoX, the master activator of competence. Hence, production of AphA markedly suppressed DNA uptake; an effect largely circumvented by ectopic expression of tfoX. Our observations suggest dual regulation of competence. At low cell density AphA is a master repressor whilst HapR activates the process at high cell density. Thus, we provide deep mechanistic insight into the role of AphA and highlight how V. cholerae utilises this regulator for diverse purposes.

A new panel of epitope mapped monoclonal antibodies recognising the prototypical tetraspanin CD81.

Background: Tetraspanins are small transmembrane proteins, found in all higher eukaryotes, that compartmentalize cellular membranes through interactions with partner proteins. CD81 is a prototypical tetraspanin and contributes to numerous physiological and pathological processes, including acting as a critical entry receptor for hepatitis C virus (HCV). Antibody engagement of tetraspanins can induce a variety of effects, including actin cytoskeletal rearrangements, activation of MAPK-ERK signaling and cell migration. However, the epitope specificity of most anti-tetraspanin antibodies is not known, limiting mechanistic interpretation of these studies. Methods: We generated a panel of monoclonal antibodies (mAbs) specific for CD81 second extracellular domain (EC2) and performed detailed epitope mapping with a panel of CD81 mutants. All mAbs were screened for their ability to inhibit HCV infection and E2-CD81 association. Nanoscale distribution of cell surface CD81 was investigated by scanning electron microscopy. Results: The antibodies were classified in two epitope groups targeting opposing sides of EC2. We observed a wide range of anti-HCV potencies that were independent of their epitope grouping, but associated with their relative affinity for cell-surface expressed CD81. Scanning electron microscopy identified at least two populations of CD81; monodisperse and higher-order assemblies, consistent with tetraspanin-enriched microdomains. Conclusions: These novel antibodies provide well-characterised tools to investigate CD81 function, including HCV entry, and have the potential to provide insights into tetraspanin biology in general.

Supramolecular structure in the membrane of Staphylococcus aureus.

All life demands the temporal and spatial control of essential biological functions. In bacteria, the recent discovery of coordinating elements provides a framework to begin to explain cell growth and division. Here we present the discovery of a supramolecular structure in the membrane of the coccal bacterium Staphylococcus aureus, which leads to the formation of a large-scale pattern across the entire cell body; this has been unveiled by studying the distribution of essential proteins involved in lipid metabolism (PlsY and CdsA). The organization is found to require MreD, which determines morphology in rod-shaped cells. The distribution of protein complexes can be explained as a spontaneous pattern formation arising from the competition between the energy cost of bending that they impose on the membrane, their entropy of mixing, and the geometric constraints in the system. Our results provide evidence for the existence of a self-organized and nonpercolating molecular scaffold involving MreD as an organizer for optimal cell function and growth based on the intrinsic self-assembling properties of biological molecules.