10671348
Structural analysis of botulinum neurotoxin serotype F light chain: implications on substrate binding and inhibitor design.
The seven serologically distinct Clostridium botulinum neurotoxins (BoNTs A-G) are zinc endopeptidases which block the neurotransmitter release by cleaving one of the three proteins of the soluble N-ethylmaleimide-sensitive-factor attachment protein receptor complex (SNARE complex) essential for the fusion of vesicles containing neurotransmitters with target membranes. These metallopeptidases exhibit unique specificity for the substrates and peptide bonds they cleave. Development of countermeasures and therapeutics for BoNTs is a priority because of their extreme toxicity and potential misuse as biowarfare agents. Though they share sequence homology and structural similarity, the structural information on each one of them is required to understand the mechanism of action of all of them because of their specificity. Unraveling the mechanism will help in the ultimate goal of developing inhibitors as antibotulinum drugs for the toxins. Here, we report the high-resolution structure of active BoNT/F catalytic domain in two crystal forms. The structure was exploited for modeling the substrate binding and identifying the S1' subsite and the putative exosites which are different from BoNT/A or BoNT/B. The orientation of docking of the substrate at the active site is consistent with the experimental BoNT/A-LC:SNAP-25 peptide model and our proposed model for BoNT/E-LC:SNAP-25.
19975781
Cloning, high level expression, purification, and crystallization of the full length Clostridium botulinum neurotoxin type E light chain.
The catalytic activity of the highly potent botulinum neurotoxins are confined to their N-terminal light chains ( approximately 50kDa). A full-length light chain for the type E neurotoxin with a C-terminal 6x His-tag, BoNT/E-LC, has been cloned in a pET-9c vector and over-expressed in BL21 (DE3) cells. BoNT/E-LC was purified to homogeneity by affinity chromatography on Ni-NTA agarose followed by exclusion chromatography using a Superdex-75 sizing column. The purified protein has very good solubility and can be stored stably at -20 degrees C; however, it seems to undergo auto-proteolysis when stored at temperature #10878;4-10 degrees C. BoNT/E-LC is active on its natural substrate, the synaptosomal associated 25kDa protein, SNAP-25, indicating that it retains a native-like conformation and therefore can be considered as a useful tool in studying the structure/function of the catalytic light chain. Recombinant BoNT/E-LC has been crystallized under five different conditions and at various pHs. Crystals diffract to better than 2.1A.
12841382
Mode of VAMP substrate recognition and inhibition of Clostridium botulinum neurotoxin F
Clostridium botulinum neurotoxins (BoNTs) cleave neuronal proteins responsible for neurotransmitter release, causing the neuroparalytic disease botulism. BoNT serotypes B, D, F and G cleave and inactivate vesicle-associated membrane protein (VAMP), each at a unique peptide bond. The specificity of BoNTs depends on the mode of substrate recognition. We have investigated the mechanism of substrate recognition of BoNT F by determining the crystal structures of its complex with two substrate-based inhibitors, VAMP 22-58/Gln58D-cysteine and 27-58/Gln58D-cysteine. The inhibitors bind to BoNT F in the canonical direction (as seen for BoNTs A and E substrates) but are positioned specifically via three major exosites away from the active site. The cysteine sulfur of the inhibitors interacts with the zinc and exists as sulfinic acid in the inhibitor VAMP 27-58/Gln58D-cysteine. Arg133 and Arg171, which form part of two separate exosites, are crucial for substrate binding and catalysis.
24638854
Structure determination of an FMN reductase from Pseudomonas aeruginosa PA01 using sulfur anomalous signal.
The availability of high-intensity synchrotron facilities, technological advances in data-collection techniques and improved data-reduction and crystallographic software have ushered in a new era in high-throughput macromolecular crystallography. Here, the de novo automated crystal structure determination at 1.28 A resolution of an NAD(P)H-dependent FMN reductase flavoprotein from Pseudomonas aeruginosa PA01-derived protein Q9I4D4 using the anomalous signal from an unusually small number of S atoms is reported. Although this protein lacks the flavodoxin key fingerprint motif [(T/S)XTGXT], it has been confirmed to bind flavin mononucleotide and the binding site was identified via X-ray crystallography. This protein contains a novel flavin mononucleotide-binding site GSLRSGSYN, which has not been previously reported. Detailed statistics pertaining to sulfur phasing and other factors contributing to structure determination are discussed. Structural comparisons of the apoenzyme and the protein complexed with flavin mononucleotide show conformational changes on cofactor binding. NADPH-dependent activity has been confirmed with biochemical assays.
556786
A novel mode of dimerization via formation of a glutamate anhydride crosslink in a protein crystal structure.
Acid anhydrides are formed by removal of water, are very active, and can react with water to form the original binary components.
205373753
SNAP-25 substrate peptide (residues 180-183) binds to but bypasses cleavage by catalytically active Clostridium botulinum neurotoxin E.
Clostridium botulinum neurotoxins are the most potent toxins to humans. The recognition and cleavage of SNAREs are prime evente in exhibiting their toxicity. We report here the crystal structure of the catalytically active full-length botulinum serotype E catalytic domain (BoNT E) in complex with SNAP-25 (a SNARE protein) substrate peptide Arg(180)-Ile(181)-Met(182)-Glu(183) (P1-P3'). It is remarkable that the peptide spanning the scissile bond binds to but bypasses cleavage by the enzyme and inhibits the catalysis fairly with K(i) approximately 69 microm. The inhibitory peptide occupies the active site of BoNT E and shows well defined electron density. The catalytic zinc and the conserved key residue Tyr(350) of the enzyme facilitate the docking of Arg(180) (P1) by interacting with its carbonyl oxygen that displaces the nucleophilic water. The general base Glu(212) side chain interacts with the main chain amino group of P1 and P1'. Conserved Arg(347) of BoNT E stabilizes the proper docking of the Ile(181) (P1') main chain, whereas the hydrophobic pockets stabilize the side chains of Ile(181) (P1') and Met(182) (P2'), and the 250 loop stabilizes Glu(183) (P3'). Structural and functional analysis revealed an important role for the P1' residue and S1' pocket in driving substrate recognition and docking at the active site. This study is the first of its kind and rationalizes the substrate cleavage strategy of BoNT E. Also, our complex structure opens up an excellent opportunity of structure-based drug design for this fast acting and extremely toxic high priority BoNT E.
5371881
Acute exacerbation of idiopathic pulmonary fibrosis: a systematic review.
Acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) is a clinical entity defined by rapid deterioration of IPF during the course of the disease that is not due to infections, pulmonary embolism, or heart failure. The condition needs to be differentiated from acute interstitial pneumonia (or Hamman-Rich syndrome), which occurs in patients with no underlying lung disease. The exact etiology and pathogenesis remain unknown, but the condition is characterized by diffuse alveolar damage (on a background of IPF) that probably occurs as a result of a massive lung injury due to some unknown etiologic agent. High-resolution computed tomography can help in prognostication and management of this condition. Once infections and other causes of worsening have been excluded, treatment involves enhanced immunosuppression with pulse doses of methylprednisolone and cytotoxic agents. Our systematic review shows that the outcome, however, is poor, with 1-month and 3-month mortality around 60% and 67%, respectively. Few studies have shown beneficial effects of cyclosporine, pirfenidone, and anticoagulants in the management and prevention of AE-IPF. The etiology, risk factors, pathogenesis, therapy, prognosis, and predictors need to be studied and the potential role of newer agents in the management and prevention of AE-IPF needs to be further clarified.
20093742
Experience with paraquat poisoning in a respiratory intensive care unit in North India.
INTRODUCTION
Paraquat poisoning is an uncommon entity in India. We report our experience of managing five patients with paraquat poisoning using immunosuppressive therapy.


METHODS
Retrospective analysis of 84 patients admitted with a diagnosis of poisoning over the last eight years was performed. The data were presented in a descriptive fashion.


RESULTS
Five (5.9 percent) out of the 84 patients were admitted with a diagnosis of paraquat poisoning. All patients were mechanically ventilated. All patients had hepatic failure with median peak bilirubin being 22.1 +/- 15.1 mg/dL (range 8.4-45.5). Four of the five patients had renal failure (median peak creatinine 3.8 +/- 1.5 mg/dL; range 3.4-11.1) requiring renal replacement therapy. All patients were treated with intravenous methylprednisolone 15 mg/kg/day for three consecutive days and intravenous cyclophosphamide 10 mg/kg/ day for two consecutive days, followed by intravenous dexamethasone 4 mg thrice a day until recovery or death. Two out of the five patients survived. Three died because of severe acute respiratory distress syndrome and multiorgan dysfunction syndrome.


CONCLUSION
Paraquat poisoning is an uncommon entity in India, and is associated with a high mortality rate. There is a potential role for immunosuppressive therapy in patients with moderate to severe poisoning.
21255298
Effects of statins on renal function.
This report reviews data on the development of proteinuria in patients with chronic kidney disease who are treated with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) for dyslipidemia. Although subgroup analyses of statin trials have shown cardiovascular benefits in subjects with chronic kidney disease, concern about statin-induced proteinuria remains high. Experimental studies have suggested that the proteinuria seen with statin treatment results from the inhibition of receptor-mediated endocytosis, the likely mechanism of protein uptake in proximal tubular cells. Transient proteinuria may signify little more than the effective inhibition of cholesterol synthesis at this site. The blockade of protein trafficking in tubular cells is thought to reduce inflammation, slow fibrosis, and diminish proteinuria in the long term. Post hoc analyses of large clinical trials in subjects without overt renal disease have generally supported this notion, showing that statins most benefit patients with the greatest baseline renal deficits. Statins have also been shown to preserve glomerular filtration rate and reduce proteinuria in subjects with nondiabetic renal disease. In conclusion, in the absence of prospective, randomized trials in renally impaired patients, the collective evidence indicates that statin therapy may slow the decrease in renal function that generally attends atherosclerotic disease. The incidence of proteinuria with potent statins is only 1% to 2% when these drugs are given in recommended doses. Several large trials are currently under way to examine the safety and efficacy of statins in renally compromised patients at high risk for cardiovascular disease.
39272838
Urinary protein binding does not affect response to furosemide in patients with nephrotic syndrome.
Response to loop diuretics in patients with nephrotic syndrome (NS) is subnormal. Studies in animal models of NS have suggested that binding of diuretic to urinary albumin is one of the mechanisms that may be operative in this diuretic resistance. To explore this hypothesis, 12 patients with NS were studied to determine whether displacement from urinary protein binding with sulfisoxazole would restore response to 120 mg of furosemide. The study was stopped after treating seven patients because it was clear that sulfizoxazole had no effect. Sodium excretion (mean +/- SD) from furosemide alone was 239 +/- 90 versus 240 +/- 115 mEq/8 h with sulfisoxazole. Sulfisoxazole had modest effects on serum pharmacokinetics of furosemide but had no effect on either the time course of furosemide urinary excretion or overall amount excreted: 49 +/- 15 mg versus 54 +/- 12 mg for furosemide alone and furosemide plus sulfisoxazole, respectively. It is concluded that urinary protein binding of loop diuretics is not a major mechanism for the diuretic resistance of NS. In turn, strategies aimed at displacing such binding are unlikely to be clinically helpful.
22178651
Prognostic Value of Circadian Blood Pressure Variation in Chronic Kidney Disease
Background: Reduced circadian variation in blood pressure (BP) has been associated with cardiovascular morbidity, mortality and accelerated progression of kidney disease, but its independent prognostic value remains unknown. Methods: Using 2 definitions, one based on dipping and the other based on BP pattern (assessed by cosinor rhythmometry), we studied the prognosis of circadian BP variation among 322 patients, 179 (56%) of whom had chronic kidney disease (CKD). Results: During a follow-up period extending for up to 8.7 years, 116 (36%) patients died and 57 (32%) patients with CKD developed end-stage renal disease (ESRD). Compared to 106 patients (33%) who were dippers, the unadjusted hazard ratio (HR) for death among non-dippers was 2.03 (95% CI 1.30–3.16, p = 0.002). However, this HR became nonsignificant [1.39 (95% CI 0.89–2.19), p = 0.15] when adjusted for age and 24-hour average systolic BP. Although non-dipping was marginally associated with ESRD [HR 1.98 (95% CI 0.996–3.92), p = 0.051], even this association was weakened when adjusted for overall 24-hour systolic BP (HR 1.67, p = 0.15). Similar to the dipping definition, the BP pattern-based definition was significantly associated with mortality (p = 0.005) but not with ESRD (p = 0.68). Compared to those ‘in-phase,’ the HR for death among those ‘out-of-phase’ was 1.86 (95% CI 1.25–2.75, p = 0.002). Although this HR when adjusted for overall mean BP remained significant, when further adjusted for age, it too became nonsignificant. Conclusion: Among elderly veterans with or without CKD, circadian variation in BP is associated with mortality, but not ESRD. However, after accounting for common clinical risk factors, this association of circadian BP variation with mortality or ESRD is abolished.