Structure–function analysis of HsiF, a gp25-like component of the type VI secretion system, in Pseudomonas aeruginosa

Bacterial pathogens use a range of protein secretion systems to colonize their host. One recent addition to this arsenal is the type VI secretion system (T6SS), which is found in many Gram-negative bacteria. The T6SS involves 12–15 components, including a ClpV-like AAA+ ATPase. Moreover, the VgrG and Hcp components have been proposed to form a puncturing device, based on structural similarity to the tail spike components gp5/gp27 and the tail tube component gp19 of the T4 bacteriophage, respectively. Another T6SS component shows similarity to a T4 phage protein, namely gp25. The gp25 protein has been proposed to have lysozyme activity. Other T6SS components do not exhibit obvious similarity to characterized T4 phage components. The genome of Pseudomonas aeruginosa contains three T6SS gene clusters. In each cluster a gene encoding a putative member of the gp25-like protein family was identified, which we called HsiF. We confirmed this similarity by analysing the structure of the P. aeruginosa HsiF proteins using secondary and tertiary structure prediction tools. We demonstrated that HsiF1 is crucial for the T6SS-dependent secretion of Hcp and VgrG. Importantly, lysozyme activity of HsiF proteins was not detectable, and we related this observation to the demonstration that HsiF1 localizes to the cytoplasm of P. aeruginosa. Finally, our data showed that a conserved glutamate, predicted to be required for proper HsiF folding, is essential for its function. In conclusion, our data confirm the central role of HsiF in the T6SS mechanism, provide information on the predicted HsiF structure, and call for reconsideration of the function of gp25-like proteins

The Salmonella SPI-2 effector SseJ exhibits eukaryotic activator-dependent phospholipase A and glycerophospholipid : cholesterol acyltransferase activity

Intracellular replication of Salmonella enterica serovar Typhimurium within membrane-bound compartments, called Salmonella-containing vacuoles, depends on the activities of several effector proteins translocated by the Salmonella pathogenicity island 2 (SPI-2)-encoded type III secretion system. The SPI-2 effector protein SseJ shows similarity at the amino acid level to several GDSL lipases with glycerophospholipid : cholesterol acyltransferase (GCAT) activity. In this study, we show that catalytic serine-dependent phospholipase A (PLA) and GCAT activity of recombinant SseJ is potentiated by factor(s) present in HeLa cells, RAW macrophages and Saccharomyces cerevisiae. SseJ activity was enhanced with increasing amounts of, or preincubation with, eukaryotic cell extracts. Analysis of the activating factor(s) shows that it is soluble and heat- and protease-sensitive. We conclude that PLA and GCAT activities of SseJ are potentiated by proteinaceous eukaryotic factor(s)

Type VI Secretion System in Pseudomonas aeruginosa: Secretion and Multimerization of VgrG Proteins

Pseudomonas aeruginosa is a Gram-negative bacterium causing chronic infections in cystic fibrosis patients. Such infections are associated with an active type VI secretion system (T6SS), which consists of about 15 conserved components, including the AAA+ ATPase, ClpV. The T6SS secretes two categories of proteins, VgrG and Hcp. Hcp is structurally similar to a phage tail tube component, whereas VgrG proteins show similarity to the puncturing device at the tip of the phage tube. In P. aeruginosa, three T6SSs are known. The expression of H1-T6SS genes is controlled by the RetS sensor. Here, 10 vgrG genes were identified in the PAO1 genome, among which three are co-regulated with H1-T6SS, namely vgrG1a/b/c. Whereas VgrG1a and VgrG1c were secreted in a ClpV1-dependent manner, secretion of VgrG1b was ClpV1-independent. We show that VgrG1a and VgrG1c form multimers, which confirmed the VgrG model predicting trimers similar to the tail spike. We demonstrate that Hcp1 secretion requires either VgrG1a or VgrG1c, which may act independently to puncture the bacterial envelope and give Hcp1 access to the surface. VgrG1b is not required for Hcp1 secretion. Thus, VgrG1b does not require H1-T6SS for secretion nor does H1-T6SS require VgrG1b for its function. Finally, we show that VgrG proteins are required for secretion of a genuine H1-T6SS substrate, Tse3. Our results demonstrate that VgrG proteins are not only secreted components but are essential for secretion of other T6SS substrates. Overall, we emphasize variability in behavior of three P. aeruginosa VgrGs, suggesting that, although very similar, distinct VgrGs achieve specific functions

GOLD 2017 treatment pathways in "real life" : an analysis of the DACCORD observational study

Introduction: The 2017 update to the Global Initiative for Obstructive Lung Disease (GOLD) strategy document includes recommendations for treatment intensification or step-down in chronic obstructive pulmonary disease (COPD), although recognises that limited supporting information is available. DACCORD is an ongoing observational, non-interventional study, recruiting patients following COPD maintenance treatment change or initiation, a subset of whom were receiving a long-acting β2-agonist (LABA) plus a long-acting muscarinic antagonist (LAMA) fixed-dose combination (FDC) on entry. Since there were no requirements in terms of prior medication (and no washout before commencing LABA/LAMA FDC), this provides an opportunity to generate "real world" data to test the GOLD 2017 recommendations. Methods: To reduce heterogeneity, the current analyses include patients receiving indacaterol/glycopyrronium at baseline, and who, prior to the study, were receiving no COPD maintenance medication ("none"), LABA or LAMA monotherapy ("mono"), LABA plus inhaled corticosteroid (ICS; "LABA/ICS"), or triple therapy ("triple"). At the baseline visit, data collected included: demographic and disease characteristics; COPD Assessment Test (CAT); and exacerbations in the 6 months prior to entry. At 3, 6, 9 and 12 months data on exacerbations were collected, with CAT recorded at 3 and 12 months. Results: A total of 2724 patients were included in the baseline analyses: 795, 954, 598 and 377 in the "none", "mono", "LABA/ICS" and "triple" subgroups, respectively. There were no clinically relevant differences in baseline demographics between the four groups. In terms of disease characteristics, the "triple" group had the highest proportion of patients with a disease duration of more than 1 year since diagnosis and with severe/very severe airflow limitation, but a similar percentage of non-exacerbators compared to the "none" group. Over the 1-year follow-up, the majority of patients in all four subgroups did not exacerbate (exacerbation rates 0.16, 0.19, 0.21, and 0.26 in the "none", "mono", "LABA/ICS" and "triple" groups, respectively). At 12 months, 61.4%, 65.0%, 71.0% and 52.4% of patients had a clinically relevant improvement in CAT score. Conclusions: Overall, the results support the GOLD recommendations in suggesting that a switch from a mono-bronchodilator or LABA plus ICS to LABA/LAMA FDC is a valid treatment option for patients with COPD. The results also validate the use of a LABA/LAMA FDC as initial maintenance treatment for COPD, and provide first "real world" evidence to support the newly added "step down" recommendation (from triple to LABA/LAMA FDC)

Dual bronchodilation vs triple therapy in the "real-life" COPD DACCORD study

Background: No observational studies have evaluated the "real-world" effectiveness of dual bronchodilation comprising a long-acting β2-agonist plus a long-acting muscarinic antagonist vs that of triple therapy (long-acting β2-agonist plus long-acting muscarinic antagonist plus inhaled corticosteroid) in COPD. Materials and methods: DACCORD is a non-interventional, observational clinical study that recruited patients following COPD maintenance therapy initiation or change in maintenance therapy between or within therapeutic class. Given the non-interventional nature of the study, the decision to initiate or change medication had to be made by the patients’ physicians prior to inclusion in DACCORD. We used a matched-pairs analysis to compare disease progression in two patient groups: those receiving dual bronchodilation vs those receiving triple therapy (each group n=1,046). Results: In two subgroups of patients matched according to a broad range of demographic and disease characteristics, over 1 year, fewer patients receiving dual bronchodilation exacerbated than those receiving triple therapy (15.5% vs 26.6%; P<0.001), with a greater improvement from baseline in COPD Assessment Test total score at 1 year (mean±SD -2.9±5.8 vs -1.4±5.5; P<0.001). When analyzed according to prior therapy, the highest rate of exacerbations was in patients on triple therapy prior to the study who remained on triple therapy. Those changing from mono-bronchodilator to dual bronchodilation had the greatest COPD Assessment Test total score improvement. Conclusion: In this "real-life" cohort of patients with COPD, most of whom had not exacerbated in the 6 months prior to entry, triple therapy did not seem to improve outcomes compared with dual bronchodilation in terms of either exacerbations or health status. Our analyses clearly demonstrate the potential impact of prior medication on study results, something that should be taken into account when interpreting the results even of controlled clinical trials

A two-year evaluation of the "real life" impact of COPD on patients in Germany : the DACCORD observational study

Introduction: DACCORD is an observational, non-interventional study being conducted in German primary and secondary care centres. The study aims to describe the impact of disease (including exacerbations) and treatments over 2 years on ‘real-life’ patients with chronic obstructive pulmonary disease (COPD). Materials and methods: Patients had a clinical and spirometry diagnosis of COPD, were aged ≥40 years and, on recruitment, were initiating or changing COPD maintenance medication. The only exclusion criteria were asthma and randomised clinical trial participation. Exacerbations data were collected every 3 months. COPD medication, COPD Assessment Test (CAT) and forced expiratory volume in 1 s (FEV1) were recorded at baseline and after 1 and 2 years. Results: A total of 6122 patients were recruited, 3137 (51.2%) of whom completed the 2-year visit. The mean age of these patients was 65.6 years, 59% were male, 69% had mild or moderate airflow limitation, and their mean COPD Assessment Test (CAT) total score was 20.3. Overall, there was a trend towards decreasing COPD exacerbation rates over the 2-year follow-up period, with rates of 0.390 during Year 1 and 0.347 during Year 2. Rates were lower in patients with no exacerbation during the 6 months prior to entry (0.263 and 0.251 during Years 1 and 2, respectively), with 51.6% of patients having no exacerbation during the 6 months prior to entry and over the 2-year follow-up. Approximately 50% of the overall population experienced a clinically relevant improvement from baseline in CAT total score at Year 1 and 2. When assessed by treatment class (or classes), persistence to medication was high (77.8% in Year 1 and 71.4% in Year 2). Conclusions: Overall, the 2-year follow-up data from DACCORD suggest that for most patients with COPD exacerbations are a rare event. For the majority of patients, the focus should be on managing symptoms, and the impact that these symptoms have on their daily lives. Even for those patients who do exacerbate, although prevention of exacerbations is an important factor, management of symptoms should be a key consideration. DACCORD also suggests that COPD disease progression is not inevitable – providing patients are receiving pharmacological treatment

Treatment response in COPD: does FEV1 say it all? A post hoc analysis of the CRYSTAL study

The association between clinically relevant changes in patient-reported outcomes (PROs) and forced expiratory volume in 1 s (FEV1) in patients with chronic obstructive pulmonary disease (COPD) has rarely been investigated. Using CRYSTAL, a 12-week open-label study in symptomatic, nonfrequently exacerbating patients with moderate COPD, we assessed at baseline the correlations between several PROs (Baseline Dyspnoea Index, modified Medical Research Council dyspnoea scale, COPD Assessment Test (CAT) and Clinical COPD Questionnaire (CCQ)), and between FEV1 and PROs. Associations between clinically relevant responses in FEV1, CAT, CCQ and Transition Dyspnoea Index (TDI) at week 12 were also assessed. Using data from 4324 patients, a strong correlation was observed between CAT and CCQ (rs=0.793) at baseline, with moderate or weak correlations between other PROs, and no correlation between FEV1 and any PRO. At week 12, 2774 (64.2%) patients were responders regarding TDI, CAT or CCQ, with 583 (13.5%) responding using all three measures. In comparison, 3235 (74.8%) were responders regarding FEV1, TDI, CAT or CCQ, with 307 (7.1%) responding concerning all four parameters. Increases in lung function were accompanied by clinically relevant improvements of PROs in a minority of patients. Our results also suggest that PROs are not interchangeable. Thus, the observed treatment success in a clinical trial may depend on the selected parameters