Lipopeptides: from self-assembly to bioactivity

This Feature Article discusses several classes of lipopeptide with important biomedical applications as antimicrobial and antifungal agents, in immune therapies and in personal care applications among others. Two main classes of lipopeptide are considered: (i) bacterially-expressed lipopeptides with a cyclic peptide headgroup and (ii) linear lipopeptides (with one or more lipid chains) based on bio-derived and bio-inspired amino acid sequences with current clinical applications. The applications are briefly summarized, and the biophysical characterization of the molecules is reviewed, with a particular focus on self-assembly. For several of these types of biomolecule, the formation of micelles above a critical micelle concentration has been observed while others form bilayer structures, depending on conditions of pH and temperature. As yet, there are few studies on the possible relationship between self-assembly into structures such as micelles and bioactivity of this class of molecule although this is likely to attract further attention.

A self-assembling fluorescent dipeptide conjugate for cell labelling

Derivatives of fluorophore FITC (fluorescein isothiocyanate) are widely used in bioassays to label proteins and cells. An N-terminal leucine dipeptide is attached to FITC, and we show that this simple conjugate molecule is cytocompatible and is uptaken by cells (human dermal and corneal fibroblasts) in contrast to FITC itself. Co-localisation shows that FITC-LL segregates in peri-nuclear and intracellular vesicle regions. Above a critical aggregation concentration, the conjugate is shown to self-assemble into beta-sheet nanostructures comprising molecular bilayers.

Self-assembly of the anti-fungal polyene amphotericin B into giant helically-twisted nanotapes

The amphiphilic polyene amphotericin B, a powerful treatment for systemic fungal infections, is shown to exhibit a critical aggregation concentration, and to form giant helically-twisted nanostructures via self-assembly in basic aqueous solution.

Erythropoietin mimics the acute phase response in critical illness

Background: In a prospective observational study, we examined the temporal relationships between serum erythropoietin (EPO) levels, haemoglobin concentration and the inflammatory response in critically ill patients with and without acute renal failure (ARF). Patients and method Twenty-five critically ill patients, from general and cardiac intensive care units (ICUs) in a university hospital, were studied. Eight had ARF and 17 had normal or mildly impaired renal function. The comparator group included 82 nonhospitalized patients with normal renal function and varying haemoglobin concentrations. In the patients, levels of haemoglobin, serum EPO, C-reactive protein, IL-1β, IL-6, serum iron, ferritin, vitamin B12 and folate were measured, and Coombs test was performed from ICU admission until discharge or death. Concurrent EPO and haemoglobin levels were measured in the comparator group. Results: EPO levels were initially high in patients with ARF, falling to normal or low levels by day 3. Thereafter, almost all ICU patients demonstrated normal or low EPO levels despite progressive anaemia. IL-6 exhibited a similar initial pattern, but levels remained elevated during the chronic phase of critical illness. IL-1β was undetectable. Critically ill patients could not be distinguished from nonhospitalized anaemic patients on the basis of EPO levels. Conclusion: EPO levels are markedly elevated in the initial phase of critical illness with ARF. In the chronic phase of critical illness, EPO levels are the same for patients with and those without ARF, and cannot be distinguished from noncritically ill patients with varying haemoglobin concentrations. Exogenous EPO therapy is unlikely to be effective in the first few days of critical illness.

Critical flux in ultrafiltration of skimmed milk

he best operating conditions, using the critical flux concept during ultrafiltration of skimmed milk, were evaluated for tubular membranes. It was found that irreversible fouling was greatly reduced by operating at or below the critical flux, but was not totally eliminated. The critical flux of skimmed milk was found to be the weak form. The critical flux at cross flow velocity 3.4 in s(-1) for MWCO 200 kDa membrane was 56.9 kg m(-2) h(-1) while for MWCO 25 kDa membranes it was 45 kg m(2) h(-1) suggesting that membrane pore size influenced the flux. The critical flux increased with increasing wall shear stress and decreased with increasing protein concentration. Empirical equations, for predicting the critical flux (J(crit)) for skimmed milk with a protein concentration (c(b)) in the range 3-7% w/w and wall shear stress (tau(w)) in the range 7-60 Pa for MWCO 200 kDa and 25 kDa membranes were J(crit) = 5.1 (tau(w)/c(b)) and J(crit) = 4.0 (tau(w)/c(b)) respectively. In general, the rejections of protein and lactose at the critical flux were not affected by protein concentration, wall shear stress and membrane used, and they were similar to those found when operating at the limiting flux.

Agonists of protease-activated receptors 1 and 2 stimulate electrolyte secretion from mouse gallbladder

Cholecystitis is one of the most common gastrointestinal diseases. Inflammation induces the activation of proteases that can signal to cells by cleaving protease-activated receptors (PARs) to induce hemostasis, inflammation, pain, and repair. However, the distribution of PARs in the gallbladder is unknown, and their effects on gallbladder function have not been fully investigated. We localized immunoreactive PAR(1) and PAR(2) to the epithelium, muscle, and serosa of mouse gallbladder. mRNA transcripts corresponding to PAR(1) and PAR(2), but not PAR(4), were detected by RT-PCR and sequencing. Addition of thrombin and a PAR(1)-selective activating peptide (TFLLRN-NH(2)) to the serosal surface of mouse gallbladder mounted in an Ussing chamber stimulated an increase in short-circuit current in wild-type but not PAR(1) knockout mice. Similarly, serosally applied trypsin and PAR(2) activating peptide (SLIGRL-NH(2)) increased short-circuit current in wild-type but not PAR(2) knockout mice. Proteases and activating peptides strongly inhibited electrogenic responses to subsequent stimulation with the same agonist, indicating homologous desensitization. Removal of HCO(3)(-) ions from the serosal buffer reduced responses to thrombin and trypsin by >80%. Agonists of PAR(1) and PAR(2) increase intracellular Ca(2+) concentration in isolated and cultured gallbladder epithelial cells. The COX-2 inhibitor meloxicam and an inhibitor of CFTR prevented the stimulatory effect of PAR(1) but not PAR(2). Thus PAR(1) and PAR(2) are expressed in the epithelium of the mouse gallbladder, and serosally applied proteases cause a HCO(3)(-) secretion. The effects of PAR(1) but not PAR(2) depend on generation of prostaglandins and activation of CFTR. These mechanisms may markedly influence fluid and electrolyte secretion of the inflamed gallbladder when multiple proteases are generated.

Full effects of land use change in the representative concentration pathways

Future land use change (LUC) is an important component of the IPCC representative concentration pathways (RCPs), but in these scenarios' radiative forcing targets the climate impact of LUC only includes greenhouse gases. However, climate effects due to physical changes of the land surface can be as large. Here we show the critical importance of including non-carbon impacts of LUC when considering the RCPs. Using an ensemble of climate model simulations with and without LUC, we show that the net climate effect is very different from the carbon-only effect. Despite opposite signs of LUC, all the RCPs assessed here have a small net warming from LUC because of varying biogeophysical effects, and in RCP4.5 the warming is outside of the expected variability. The afforestation in RCP4.5 decreases surface albedo, making the net global temperature anomaly over land around five times larger than RCPs 2.6 and 8.5, for around twice the amount of LUC. Consequent changes to circulation in RCP4.5 in turn reduce Arctic sea ice cover. The small net positive temperature effect from LUC could make RCP4.5's universal carbon tax, which incentivizes retaining and growing forest, counter productive with respect to climate. However, there are spatial differences in the balance of impacts, and potential climate gains would need to be assessed against other environmental aims.