Heterochiral tetrapeptide self-assembly into hydrogel biomaterials for hydrolase mimicry

Self-assembling short peptides have attracted great interest as enzyme mimics, especially if the catalytic activity resides solely in the supramolecular structure so that it can be switched on/off as needed by controlling assembly/disassembly. Among the various enzyme classes, hydrolases find wide application in biomaterials, and their mimetics often contain His residues, in addition to either divalent cations or other amino acids to mimic the catalytic site. This work reports two self-assembling tetrapeptides based on the Ser-His motif for catalysis and the Phe-Phe motif to drive amyloid structure formation. Both peptides form thermoreversible hydrogels in phosphate buffer at neutral pH that display a mild esterase-like activity, as demonstrated on the hydrolysis of 4-nitrophenyl acetate as a model substrate, although presence of Ser did not enhance catalytic activity. The systems are characterised by circular dichroism, transmission electron microscopy, oscillatory rheology and Thioflavin T fluorescence as an amyloid stain, to provide further insights that may assist the future design of improved supramolecular catalysts.     

Developmental staging table of the green iguana

Embryonic staging tables provide information to standardize embryological investigations and to subsidize discussions about evolution. We have established a developmental staging table for Iguana iguana iguana. The sample was composed of 142 embryos, incubated at a constant temperature and collected at regular intervals. Morphological features as pharyngeal arches, craniofacial structures, eyes, limbs, claws, pigmentation, scales and egg tooth were evaluated to determine development stages. The normal staging table includes 17 stages from oviposition to hatching, based on chronology and morphological external features. Stages from 1 to 27 occur before oviposition. Stage 28 was the first described, because all embryos presented limb bud anlage, key feature of the previous stage. We used pharyngeal arches and limb buds to describe the first stages; claws, genital papilla and scales to describe the middle stages; and pigmentation, size and egg tooth to describe the last stages. Incubation lasted approximately 2 months in a controlled environment. The results were similar to the data from other lizards, confirming the embryonic conservative pattern of the group.     

Small-angle neutron and X-ray scattering analysis of the supramolecular organization of rhodopsin in photoreceptor membrane

The supramolecular organization of the visual pigment rhodopsin in the photoreceptor membrane remains contentious. Specifically, whether this G protein-coupled receptor functions as a monomer or dimer remains unknown, as does the presence or absence of ordered packing of rhodopsin molecules in the photoreceptor membrane. Completely opposite opinions have been expressed on both issues. Herein, using small-angle neutron and X-ray scattering approaches, we performed a comparative analysis of the structural characteristics of the photoreceptor membrane samples in buffer, both in the outer segment of photoreceptor cells, and in the free photoreceptor disks. The average distance between the centers of two neighboring rhodopsin molecules was found to be ~5.8 nm in both cases. The results indicate an unusually high packing density of rhodopsin molecules in the photoreceptor membrane, but molecules appear to be randomly distributed in the membrane without any regular ordering.     

A field portable method for the semi‐quantitative estimation of dehydration tolerance of photosynthetic tissues across distantly related land plants

Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (F_v/fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt‐solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50–200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial F_v/fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi‐quantitative expression of DHT that facilitates comparisons of species with different morpho‐physiological traits and/or ecological attributes.     

Spontaneous meningoencephalitis by Staphylococcus aureus in an infant golden‐headed lion tamarin (Leontopithecus chrysomelas)

Non‐human primates are susceptible to many bacteria, some of which bear zoonotic potential. We report the pathologic features of spontaneous fulminating meningoencephalitis by Staphylococcus aureus in a captive infant golden‐headed lion tamarin (Leontopithecus chrysomelas) from Brazil.     

Mechanisms of plant protection against two oxalate-producing fungal pathogens by oxalotrophic strains of Stenotrophomonas spp.

Plant Molecular Biology - Oxalotrophic Stenotrophomonas isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including...     

GABAA Modulation of S100B Secretion in Acute Hippocampal Slices and Astrocyte Cultures

Astrocytes are the major glial cells in brain tissue and are involved, among many functions, ionic and metabolic homeostasis maintenance of synapses. These cells express receptors and transporters for neurotransmitters, including GABA. GABA signaling is reportedly able to affect astroglial response to injury, as evaluated by specific astrocyte markers such as glial fibrillary acid protein and the calcium-binding protein, S100B. Herein, we investigated the modulatory effects of the GABA_A receptor on astrocyte S100B secretion in acute hippocampal slices and astrocyte cultures, using the agonist, muscimol, and the antagonists pentylenetetrazol (PTZ) and bicuculline. These effects were analyzed in the presence of tetrodotoxin (TTX), fluorocitrate (FLC), cobalt and barium. PTZ positively modify S100B secretion in hippocampal slices and astrocyte cultures; in contrast, bicuculline inhibited S100B secretion only in hippocampal slices. Muscimol, per se, did not change S100B secretion, but prevented the effects of PTZ and bicuculline. Moreover, PTZ-induced S100B secretion was prevented by TTX, FLC, cobalt and barium indicating a complex GABA_A communication between astrocytes and neurons. The effects of two putative agonists of GABA_A, β-hydroxybutyrate and methylglyoxal, on S100B secretion were also evaluated. In view of the neurotrophic role of extracellular S100B under conditions of injury, our data reinforce the idea that GABA_A receptors act directly on astrocytes, and indirectly on neurons, to modulate astroglial response.

     

Matrix metalloproteinases as target genes for gene regulatory networks driving molecular and cellular pathways related to a multistep pathogenesis of cerebrovascular disease

The present study investigated a joint contribution of matrix metalloproteinases (MMPs) genes to ischemic stroke (IS) development and analyzed interactions between MMP genes and genome-wide associated loci for IS. A total of 1288 unrelated Russians (600 IS patients and 688 healthy individuals) from Central Russia were recruited for the study. Genotyping of seven single nucleotide polymorphisms (SNPs) of MMP genes (rs1799750, rs243865, rs3025058, rs11225395, rs17576, rs486055, and rs2276109) and eight genome-wide associated loci for IS were done using Taq-Man–based assays and MALDI-TOF mass spectrometry iPLEX platform, respectively. Allele − 799T at rs11225395 of the MMP8 gene was significantly associated with a decreased risk of IS after adjustment for sex and age (OR = 0.82; 95%CI, 0.70-0.96; P = 0.016). The model-based multifactor dimensionality reduction method has revealed 21 two-order, 124 three-order, and 474 four-order gene-gene (G×G) interactions models meaningfully (P_perm < 0.05) associated with the IS risk. The bioinformatic analysis enabled establishing the studied MMP gene polymorphisms possess a clear regulatory potential and may be targeted by gene regulatory networks driving molecular and cellular pathways related to the pathogenesis of IS. In conclusion, the present study was the first to identify an association between polymorphism rs11225395 of the MMP8 gene and IS risk. The study findings also indicate that MMPs deserve special attention as a potential class of genes influencing the multistep mechanisms of cerebrovascular disease including atherosclerosis in cerebral arteries, acute cerebral artery occlusion as well as the ischemic injury of the brain and its recovery.