The putative bioactive surface of insect-selective scorpion excitatory neurotoxins

Scorpion neurotoxins of the excitatory group show total specificity for insects and serve as invaluable probes for insect sodium channels. However, despite their significance and potential for application in insect-pest control, the structural basis for their bioactivity is still unknown. We isolated, characterized, and expressed an atypically long excitatory toxin, Bj-xtrIT, whose bioactive features resembled those of classical excitatory toxins, despite only 49% sequence identity. With the objective of clarifying the toxic site of this unique pharmacological group, Bj-xtrIT was employed in a genetic approach using point mutagenesis and biological and structural assays of the mutant products. A primary target for modification was the structurally unique C-terminal region. Sequential deletions of C-terminal residues suggested an inevitable significance of Ile73 and Ile74 for toxicity. Based on the bioactive role of the C-terminal region and a comparison of Bj-xtrIT with a Bj-xtrIT-based model of a classical excitatory toxin, AaHIT, a conserved surface comprising the C terminus is suggested to form the site of recognition with the sodium channel receptor.     

Lifelong cytomegalovirus and early‐LIFE irradiation synergistically potentiate age‐related defects in response to vaccination and infection

While whole‐body irradiation (WBI) can induce some hallmarks of immune aging, (re)activation of persistent microbial infection also occurs following WBI and may contribute to immune effects of WBI over the lifespan. To test this hypothesis in a model relevant to human immune aging, we examined separate and joint effects of lifelong latent murine cytomegalovirus (MCMV) and of early‐life WBI over the course of the lifespan. In late life, we then measured the response to a West Nile virus (WNV) live attenuated vaccine, and lethal WNV challenge subsequent to vaccination. We recently published that a single dose of non‐lethal WBI in youth, on its own, was not sufficient to accelerate aging of the murine immune system, despite widespread DNA damage and repopulation stress in hematopoietic cells. However, 4Gy sub‐lethal WBI caused manifest reactivation of MCMV. Following vaccination and challenge with WNV in the old age, MCMV‐infected animals experiencing 4Gy, but not lower, dose of sub‐lethal WBI in youth had reduced survival. By contrast, old irradiated mice lacking MCMV and MCMV‐infected, but not irradiated, mice were both protected to the same high level as the old non‐irradiated, uninfected controls. Analysis of the quality and quantity of anti‐WNV immunity showed that higher mortality in MCMV‐positive WBI mice correlated with increased levels of MCMV‐specific immune activation during WNV challenge. Moreover, we demonstrate that infection, including that by WNV, led to MCMV reactivation. Our data suggest that MCMV reactivation may be an important determinant of increased late‐life mortality following early‐life irradiation and late‐life acute infection.     

The effect of end‐group substitution on surface self‐assembly of peptides

Biofouling, the undesirable accumulation of organisms onto surfaces, affects many areas including health, water, and energy. We previously designed a tripeptide that self‐assembles into a coating that prevents biofouling. The peptide comprises three amino acids: DOPA, which allows its adhesion to the surface, and two fluorinated phenylalanine residues that direct its self‐assembly into a coating and acquire it with antifouling properties. This short peptide has an ester group at its C‐terminus. To examine the importance of this end group for the self‐assembly and antifouling properties of the peptide, we synthesized and characterized tripeptides with different end groups (ester, amide, or carboxylic group). Our results indicate that different groups at the C‐terminus of the peptide can lead to a change in the peptide assembly on the surface and its adsorption process. However, this change only affects the antifouling properties of the coating toward Gram‐positive bacteria (Staphylococcus epidermidis), whereas Gram‐negative bacteria (Escherichia coli) are not affected.     

Grafting of features of cystatins C or B into the N-terminal region or second binding loop of cystatin A (stefin A) substantially enhances inhibition of cysteine proteinases

Replacement of the three N-terminal residues preceding the conserved Gly of cystatin A by the corresponding 10-residue long segment of cystatin C increased the affinity of the inhibitor for the major lysosomal cysteine proteinase, cathepsin B, by approximately 15-fold. This tighter binding was predominantly due to a higher overall association rate constant. Characterization of the interaction with an inactive Cys29 to Ala variant of cathepsin B indicated that the higher rate constant was a result of an increased ability of the N-terminal region of the chimeric inhibitor to promote displacement of the cathepsin B occluding loop in the second binding step. The low dissociation rate constant for the binding of cystatin A to cathepsin B was retained by the chimeric inhibitor, which therefore had a higher affinity for this enzyme than any natural cystatin identified so far. In contrast, the N-terminal substitution negligibly affected the ability of cystatin A to inhibit papain. However, substitutions of Gly75 in the second binding loop of cystatin A by Trp or His, making the loop similar to those of cystatins C or B, respectively, increased the affinity for papain by approximately 10-fold. This enhanced affinity was due to both a higher association rate constant and a lower dissociation rate constant. Modeling of complexes between the two variants and papain indicated the possibility of favorable interactions being established between the substituting residues and the enzyme. The second-loop substitutions negligibly affected or moderately reduced the affinity for cathepsin B. Together, these results show that the inhibitory ability of cystatins can be substantially improved by protein engineering.     

KCNK?: opening and closing the 2-P-domain potassium leak channel entails "C-type" gating of the outer pore.

Essential to nerve and muscle function, little is known about how potassium leak channels operate. KCNK? opens and closes in a kinase-dependent fashion. Here, the transition is shown to correspond to changes in the outer aspect of the ion conduction pore. Voltage-gated potassium (VGK) channels open and close via an internal gate; however, they also have an outer pore gate that produces "C-type" inactivation. While KCNK? does not inactivate, KCNK? and VGK channels respond in like manner to outer pore blockers, potassium, mutations, and chemical modifiers. Structural relatedness is confirmed: VGK residues that come close during C-type gating predict KCNK? sites that crosslink (after mutation to cysteine) to yield channels controlled by reduction and oxidization. We conclude that similar outer pore gates mediate KCNK? opening and closing and VGK channel C-type inactivation despite their divergent structures and physiological roles.     

Opening and closing of KCNKO potassium leak channels is tightly regulated

Potassium-selective leak channels control neuromuscular function through effects on membrane excitability. Nonetheless, their existence as independent molecular entities was established only recently with the cloning of KCNKO from Drosophila melanogaster. Here, the operating mechanism of these 2 P domain leak channels is delineated. Single KCNKO channels switch between two long-lived states (one open and one closed) in a tenaciously regulated fashion. Activation can increase the open probability to approximately 1, and inhibition can reduce it to approximately 0.05. Gating is dictated by a 700-residue carboxy-terminal tail that controls the closed state dwell time but does not form a channel gate; its deletion (to produce a 300-residue subunit with two P domains and four transmembrane segments) yields unregulated leak channels that enter, but do not maintain, the closed state. The tail integrates simultaneous input from multiple regulatory pathways acting via protein kinases C, A, and G.     

Randomized,Double-Blind,Placebo-Controlled Study on Decolonization Procedures for Methicillin-Resistant Staphylococcus aureus (MRSA) among HIV-Infected Adults

BackgroundHIV-infected persons have increased risk of MRSA colonization and skin and soft-tissue infections (SSTI). However, no large clinical trial has examined the utility of decolonization procedures in reducing MRSA colonization or infection among community-dwelling HIV-infected persons.Methods550 HIV-infected adults at four geographically diverse US military HIV clinics were prospectively screened for MRSA colonization at five body locations every 6 months during a 2-year period. Those colonized were randomized in a double-blind fashion to nasal mupirocin (Bactroban) twice daily and hexachlorophene (pHisoHex) soaps daily for 7 days compared to placeboes similar in appearance but without specific antibacterial activity. The primary endpoint was MRSA colonization at 6-months post-randomization; secondary endpoints were time to MRSA clearance, subsequent MRSA infections/SSTI, and predictors for MRSA clearance at the 6-month time point.ResultsForty-nine (9%) HIV-infected persons were MRSA colonized and randomized. Among those with 6-month colonization data (80% of those randomized), 67% were negative for MRSA colonization in both groups (p = 1.0). Analyses accounting for missing 6-month data showed no significant differences could have been achieved. In the multivariate adjusted models, randomization group was not associated with 6-month MRSA clearance. The median time to MRSA clearance was similar in the treatment vs. placebo groups (1.4 vs. 1.8 months, p = 0.35). There was no difference on subsequent development of MRSA infections/SSTI (p = 0.89). In a multivariable model, treatment group, demographics, and HIV-specific factors were not predictive of MRSA clearance at the 6-month time point.ConclusionA one-week decolonization procedure had no effect on MRSA colonization at the 6-month time point or subsequent infection rates among community-dwelling HIV-infected persons. More aggressive or novel interventions may be needed to reduce the burden of MRSA in this population.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00631566","term_id":"NCT00631566"}}NCT00631566     

The EDD E3 ubiquitin ligase ubiquitinates and up-regulates beta-catenin

Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. β-Catenin activity is tightly regulated via a multiprotein complex that includes the kinase glycogen synthase kinase-3β (GSK-3β). GSK-3β phosphorylates β-catenin, marking it for ubiquitination and degradation via the proteasome. Thus in regulation of the Wnt pathway, the ubiquitin system is known to be involved mostly in mediating the turnover of β-catenin, resulting in reduced Wnt signaling levels. Here we report that an arm of the ubiquitin system increases β-catenin protein levels. We show that GSK-3β directly interacts with the E3 ubiquitin ligase identified by differential display (EDD) that also binds β-catenin. Expression of EDD leads to enhanced nuclear accumulation of both GSK-3β and β-catenin and results in up-regulation of β-catenin expression levels and activity. Importantly, EDD ubiquitinates β-catenin through Lys29- or Lys11-linked ubiquitin chains, leading to enhanced stability of β-catenin. Our results demonstrate a role for the ubiquitin system in up-regulation of the Wnt signaling pathway, suggesting that EDD could function as a colorectal oncogene.