Metric mechanics with nontrivial topology: Actuating irises, cylinders, and evertors.

Liquid crystal elastomers contract along their director on heating and recover on cooling, offering great potential as actuators and artificial muscles. If a flat sheet is programed with a spatially varying director pattern, then it will actuate into a curved surface, allowing the material to act as a strong machine such as a grabber or lifter. Here we study the actuation of programed annular sheets which, owing to their central hole, can sidestep constraints on area and orientation. We systematically catalog the set of developable surfaces encodable via axisymmetric director patterns and uncover several qualitatively new modes of actuation, including cylinders, irises, and everted surfaces in which the inner boundary becomes the outer boundary after actuation. We confirm our designs with a combination of experiments and numerics. Many of our actuators can reattain their initial inner or outer radius upon completing actuation, making them particularly promising, as they can avoid potentially problematic stresses in their activated state even when fixed onto a frame or pipe.

Marathon pacing ability: Training characteristics and previous experience.

Abstract Even pacing within the marathon has been associated with faster marathon performance times, however, little literature has investigated the association between pacing ability during a marathon and a recreational marathoner's training characteristics and previous experiences. N = 139 participants completed an online questionnaire concerning training history in relation to a 2017 marathon and previous long-distance running experiences. Online databases were used to collect split times of the participants after successfully completing a 2017 marathon, identifying the percentage slowdown in pace between the first half and second half of the marathon, used for correlational analyses. The strongest correlates for pacing ability were marathon finishing time and previous distance race personal best finishing times (i.e. marathon, half-marathon, 10 and 5 km). There were many weaker, however significant correlates for training history characteristics and previous long-distance running experience. The current findings demonstrate that greater accrued long-distance running experiences and higher weekly training volumes are strongly associated with smaller declines in pace during the second half of the marathon in comparison to the first half and less variability in pace during the marathon.

Antiviral activity of a standardized root water extract of Eurycoma longifolia (Physta®) against dengue virus.

The aim of this study was to investigate the antiviral property of Eurycoma longifolia Jack (EL) against dengue virus. A propriety standardized extract of Eurycoma longifolia Jack (Physta®) was tested for anti-viral activity after viral adsorption in Vero cell line. Viral yield was measured by qRT-PCR in four serotypes of dengue virus. The antiviral activity was further investigated in an in vivo AG129 mouse model for dengue inhibitory candidates. 100 mg/kg EL extract was fed twice daily and challenged with a lethal dose of (~1x105 PFU per mouse) of DENV-2 over a period of six days. Antiviral activity with IC50 of 33.84, 33.55, 58.35 and 119 µg/ml for DENV-1, DENV-2, DENV-3 and DENV-4 serotypes respectively was observed. The selectivity index (SI) values determined as the ratio of cytotoxic concentration (CC50) to inhibitory concentration (IC50) was the lowest for DENV-2 at 28.9. The dengue virus (DENV) replication measured by qRT-PCR showed a reduction of 100% for DENV-1, DENV-2, DENV-3 and 80% for DENV-4 at day 2 of exposure. In the in vivo AG129 mouse model, a lower weight reduction, 30% lower viral load and 12% higher platelet in the extract group compared to the control was observed at day 6. The extract of E. longifolia has potential anti-dengue properties with improving trends in platelet counts. E. longifolia supplementation is potentially a two-pronged approach in treating dengue fever.

Antiviral activity of a standardized root water extract of Eurycoma longifolia (Physta®) against dengue virus

@#The aim of this study was to investigate the antiviral property of Eurycoma longifolia Jack (EL) against dengue virus. A propriety standardized extract of Eurycoma longifolia Jack (Physta®) was tested for anti-viral activity after viral adsorption in Vero cell line. Viral yield was measured by qRT-PCR in four serotypes of dengue virus. The antiviral activity was further investigated in an in vivo AG129 mouse model for dengue inhibitory candidates. 100 mg/kg EL extract was fed twice daily and challenged with a lethal dose of (~1x105 PFU per mouse) of DENV-2 over a period of six days. Antiviral activity with IC50 of 33.84, 33.55, 58.35 and 119 μg/ml for DENV-1, DENV-2, DENV-3 and DENV-4 serotypes respectively was observed. The selectivity index (SI) values determined as the ratio of cytotoxic concentration (CC50) to inhibitory concentration (IC50) was the lowest for DENV-2 at 28.9. The dengue virus (DENV) replication measured by qRT-PCR showed a reduction of 100% for DENV-1, DENV-2, DENV-3 and 80% for DENV-4 at day 2 of exposure. In the in vivo AG129 mouse model, a lower weight reduction, 30% lower viral load and 12% higher platelet in the extract group compared to the control was observed at day 6. The extract of E. longifolia has potential anti-dengue properties with improving trends in platelet counts. E. longifolia supplementation is potentially a two-pronged approach in treating dengue fever.

Surface sulci in squeezed soft solids.

The squeezing of soft solids, the constrained growth of biological tissues, and the swelling of soft elastic solids such as gels can generate large compressive stresses at their surfaces. This causes the otherwise smooth surface of such a solid to become unstable when its stress exceeds a critical value. Previous analyses of the surface instability have assumed two-dimensional plane-strain conditions, but in experiments isotropic stresses often lead to complex three-dimensional sulcification patterns. Here we show how such diverse morphologies arise by numerically modeling the lateral compression of a rigidly clamped elastic layer. For incompressible solids, close to the instability threshold, sulci appear as I-shaped lines aligned orthogonally with their neighbors; at higher compressions they are Y-shaped and prefer a hexagonal arrangement. In contrast, highly compressible solids when squeezed show only one sulcified phase characterized by a hexagonal sulcus network.

Characterization of soft stripe-domain deformations in Sm-C and Sm-C* liquid-crystal elastomers.

The neoclassical model of Sm-C (and Sm-C*) elastomers developed by Warner and Adams predicts a class of "soft" (zero energy) deformations. We find and describe the full set of stripe domains-laminate structures in which the laminates alternate between two different deformations-that can form between pairs of these soft deformations. All the stripe domains fall into two classes, one in which the smectic layers are not bent at the interfaces, but for which--in the Sm-C* case--the interfaces are charged, and one in which the smectic layers are bent but the interfaces are never charged. Striped deformations significantly enhance the softness of the macroscopic elastic response.

Supersoft elasticity in polydomain nematic elastomers.

We consider the equilibrium stress-strain behavior of polydomain liquid crystal elastomers (PLCEs). We show that there is a fundamental difference between PLCEs cross-linked in the high temperature isotropic and low temperature aligned states. PLCEs cross-linked in the isotropic state then cooled to an aligned state will exhibit extremely soft elasticity (confirmed by recent experiments) and ordered director patterns characteristic of textured deformations. PLCEs cross-linked in the aligned state will be mechanically much harder and characterized by disclination textures.

Semisoft elastic response of nematic elastomers to complex deformations.

We consider a relaxed semisoft elastomer with its director oriented along the z axis that is first subjected to a large stretch in the x direction then to a slight x-z shear. We give a general argument that in any theory including director rotation, at the onset and end of the director rotation induced by these large stretches, there will be kinks in the stress-large strain curve (forming a stress-strain plateau) and zeros in the x-z shear modulus (C5) associated with small shears imposed on top of the stretches. We then find the analytical forms of the C5 -strain curves for a particular model of semisoftness (arising from compositional fluctuations) and show that it, together with the known stress-strain curve, provides the basis for a strong test of this theory. Finally, we consider the scope for other semisoft models and show that the compositional fluctuations model in fact yielded a generic form, that is, it is the most general quadratic free energy that does not explicitly include a final state direction other than the director. By introducing such additional directions, a large range of alternative models could be developed.

Nontransitivity of paternity in a bird.

In many animals reproductive success is determined after insemination by the interaction of male and female processes. While sperm competition is reasonably well understood in some taxa, other processes, such as cryptic female choice and differential early embryo mortality resulting from genetic incompatibilities, are less well understood. The relative importance of these different factors contributing to reproductive success is difficult to assess. Here we control for male-mediated effects (which are often considerable and can mask more subtle processes) through the artificial insemination of known numbers of sperm in the domestic fowl to reveal that male reproductive success is nontransitive across females: the success of a particular male depends on the background against which his sperm compete for fertilization. Two potential processes could account for this effect: cryptic female choice (sperm choice) or differential early embryo mortality. Regardless of the mechanism, nontransitivity of male reproductive success has important evolutionary consequences, including the maintenance of variation in male fitness.

Structure, mechanism and engineering of a nucleotidylyltransferase as a first step toward glycorandomization.

Metabolite glycosylation is affected by three classes of enzymes: nucleotidylyltransferases, which activate sugars as nucleotide diphospho-derivatives, intermediate sugar-modifying enzymes and glycosyltransferases, which transfer the final derivatized activated sugars to aglycon substrates. One of the first crystal structures of an enzyme responsible for the first step in this cascade, alpha-D-glucopyranosyl phosphate thymidylyltransferase (Ep) from Salmonella, in complex with product (UDP-Glc) and substrate (dTTP) is reported at 2.0 A and 2.1 A resolution, respectively. These structures, in conjunction with the kinetic characterization of Ep, clarify the catalytic mechanism of this important enzyme class. Structure-based engineering of Ep produced modified enzymes capable of utilizing 'unnatural' sugar phosphates not accepted by wild type Ep. The demonstrated ability to alter nucleotidylyltransferase specificity by design is an integral component of in vitro glycosylation systems developed for the production of diverse glycorandomized libraries.

Developments in the care of patients who require surgery for an abscess.

This is the first of a series of three articles which won the Alison Bell Writer's Award this year. Jill Biggins won first prize for this article which looks at a way of improving the patient's experience of day surgery. The Writer's Award is sponsored by NATN and Regent Medical.

A continuous assay for DNA cleavage: the application of "break lights" to enediynes, iron-dependent agents, and nucleases.

Although extensive effort has been applied toward understanding the mechanism by which enediynes cleave DNA, a continuous assay for this phenomenon is still lacking. In fact, with the exception of assays for DNase, continuous assays for most DNA cleavage events are unavailable. This article describes the application of "molecular break lights" (a single-stranded oligonucleotide that adopts a stem-and-loop structure and carries a 5'-fluorescent moiety, a 3'-nonfluorescent quenching moiety, and an appropriate cleavage site within the stem) to develop the first continuous assay for cleavage of DNA by enediynes. Furthermore, the generality of this approach is demonstrated by using the described assay to directly compare the DNA cleavage by naturally occurring enediynes [calicheamicin and esperamicin), non-enediyne small molecule agents (bleomycin, methidiumpropyl-EDTA-Fe(II), and EDTA-Fe(II]), as well as the restriction endonuclease BamHI. Given the simplicity, speed, and sensitivity of this approach, the described methodology could easily be extended to a high throughput format and become a new method of choice in modern drug discovery to screen for novel protein-based or small molecule-derived DNA cleavage agents.

Introduction of a [4Fe-4S (S-cys)4]+1,+2 iron-sulfur center into a four-alpha helix protein using design parameters from the domain of the Fx cluster in the Photosystem I reaction center.

We describe the insertion of an iron-sulfur center into a designed four alpha-helix model protein. The model protein was re-engineered by introducing four cysteine ligands required for the coordination of the mulinucleate cluster into positions in the main-chain directly analogous to the domain predicted to ligand the interpeptide [4Fe-4S (S-cys)4] cluster, Fx, from PsaA and PsaB of the Photosystem I reaction center. This was achieved by inserting the sequence, CDGPGRGGTC, which is conserved in PsaA and PsaB, into interhelical loops 1 and 3 of the four alpha-helix model. The holoprotein was characterized spectroscopically after insertion of the iron-sulfur center in vitro. EPR spectra confirmed the cluster is a [4Fe-4S] type, indicating that the cysteine thiolate ligands were positioned as designed. The midpoint potential of the iron-sulfur center in the model holoprotein was determined via redox titration and shown to be -422 mV (pH 8.3, n = 1). The results support proposals advanced for the structure of the domain of the [4Fe-4S] Fx cluster in Photosystem I based upon sequence predictions and molecular modeling. We suggest that the lower potential of the Fx cluster is most likely due to factors in the protein environment of Fx rather than the identity of the residues proximal to the coordinating ligands.

Site-directed mutagenesis of the subunit PsaC establishes a surface-exposed domain interacting with the photosystem I core binding site.

We have postulated that the orientation of PsaC on the photosystem I core involves electrostatic interactions between charged residues on the core binding site and the subunit [Rodday, S. M., Jun, S.-S., & Biggins, J. (1993) Photosynth. Res. 36, 1-9]. We, therefore, changed eight acidic residues on PsaC to arginine and examined the efficiency of the mutant subunits in the reconstitution of P700-Fx cores in vitro. Reconstitution of the cores by the mutant subunits was determined by analysis of the kinetics of recombination reactions between P700+ and reduced acceptors as measured optically. Restoration of complete forward electron transfer, indicative of efficient subunit binding, was estimated from the ca. 30 ms decay component in the flash transients. Slightly reduced levels of reconstitution were observed for the mutants D24R, E46R/D47R. D61R, and E72R. In contrast, mutants D9R, E27R, and D32R showed significantly lower efficiencies. The presence of the iron-sulfur centers, FA and FB, in these three mutant subunits was confirmed by low-temperature EPR spectroscopy indicating that the polypeptides had folded correctly. We conclude that the introduction of positively charged side chains at positions 9, 27, and 32 seriously disrupts PsaC binding. However, when the wild-type acidic residues in these positions were changed to alanine, only mutant D9A showed a reduced level of reconstitution, suggesting that this aspartate is the most important residue participating in the electrostatic interaction with the core. The results are discussed in relation to the photosystem I crystal structure and support an orientation of PsaC on the core such that center FB is proximal to Fx.

Evidence that the FX domain in photosystem I interacts with the subunit PsaC: site-directed changes in PsaB destabilize the subunit interaction in Chlamydomonas reinhardtii.

The highly conserved amino acid sequence PCDGPGRGGTC in both photosystem I reaction center core proteins PsaA and PsaB has been predicted to contribute the four cysteine ligands for coordination of the 4Fe-4S iron-sulfur cluster FX, and we have proposed a working model for the binding of PsaC to this domain of the reaction center core heterodimer [Rodday et al. (1993) Photosynth. Res. 36, 1-9]. We have investigated structure-function relationships between this domain and the PsaC subunit by site-directed mutagenesis of the conserved prolines P560 and P564, and the charged residues D562 and R566 in the eucaryotic alga Chlamydomonas reinhardtii. The D562N and R566E mutants did not accumulate the PsaA and PsaB reaction center proteins, indicating that these residues are essential for the stable assembly of photosystem I. The P560A, P560L, and P564L mutants accumulated functional reaction centers but showed an impaired interaction between the reaction center core complex and the PsaC subunit. We observed that the reaction centers of the proline mutants dissociated more readily in urea, and reconstitution of the mutant core preparations using PsaC and Fe-S cluster insertion protocols in vitro were incomplete. We suggest that P560 and D562 contribute to the stability of the FX cluster, most likely by providing essential hydrogen bonding to the C561 ligand. The data obtained from the P564 and R566 replacements provide direct evidence that the intercysteinyl region in PsaB is a domain involved in the interaction between PsaC and the reaction center core.

Structure-function studies on the interaction of PsaC with the Photosystem 1 heterodimer : The site directed change R561E in PsaB destabilizes the subunit interaction in Synechocystis sp. PCC 6803.

The interaction of PsaC with the core heterodimer of Photosystem 1 was studied in wild type Synechocystis sp. PCC 6803 and the site-directed mutant R561E of PsaB. The mutant reaction center was much less stable in urea and the functional reconstitution of the mutant core using PsaC was impaired. However, the extent of reconstitution increased in the presence of divalent cations whereas that of the wild type was inhibited. We conclude that the reaction center in the mutant is unstable, most likely due to the introduction of an unfavorable electrostatic interaction between surface-exposed residues on PsaC and the binding site for the subunit on the core heterodimer in support of the model proposed previously (Rodday et al. (1993) Photosynth Res 36: 1-9).

Interaction of the FAF B-containing subunit with the Photosystem 1 core heterodimer.

The structure of the predicted amino acid sequence in the FX domain of Photosystem 1 was studied by molecular modeling and a working hypothesis was developed for the functional interaction of PsaC with the core heterodimer. We propose that the intervening sequences between homologous cysteines in the FX cluster form two flexible loops and participate in the binding of PsaC, and that the arginine residues in the two surface-exposed loops may promote the interaction between the P700-FX core and the subunit. The model was tested experimentally; chemical modification of arginine residues in the P700-FX core using phenylglyoxal prevented reconstitution of the core with PsaC and PsaD after insertion of FeS clusters in vitro. Treatment of the P700-FX core with trypsin also prevented reconstitution of terminal electron transfer to FAFB, although neither treatments affected the electron transfer to FX as judged by flash kinetic spectrophotometry. Electron transfer in the P700-FAFB complex was not impaired by either phenylglyoxal or trypsin treatment indicating that the small subunit(s) protect the arginine residues that become chemically modified or cleaved. The data are consistent with the working model and point to additional experiments designed to identify the specific residues involved in the interaction between the P700-FX core and PsaC.

Human brain peptidase activity with the specificity to generate the N-terminus of the Alzheimer beta-amyloid protein from its precursor.

The synthetic peptide acetyl-Glu-Val-Lys-Met-Asp-Ala-Glu-Phe-NH2, which spans the cleavage site (Met-Asp) required to generate the N-terminus of the Alzheimer beta-amyloid protein from its precursor, was used to search for human brain peptidases which may be involved in this potentially amyloidogenic process. In both soluble and particulate fractions from human brain the primary cleavage point of the peptide was the Met-Asp bond. Purification and characterization of the activity from the soluble fraction showed that it was metalloendopeptidase 24.15 (EC3.4.24.15). This enzyme is therefore a candidate for the generation of the N-terminus of beta-amyloid protein from its precursor.