Tyrosine's Unique Role in the Hierarchical Assembly of Recombinant Spider Silk Proteins: From Spinning Dope to Fibers

Producing recombinant spider silk fibers that exhibit mechanical properties approaching native spider silk is highly dependent on the constitution of the spinning dope. Previously published work has shown that recombinant spider silk fibers spun from dopes with phosphate-induced pre-assembly (biomimetic dopes) display a toughness approaching native spider silks far exceeding the mechanical properties of fibers spun from dopes without pre-assembly (classical dopes). Dynamic light scattering experiments comparing the two dopes reveal that biomimetic dope displays a systematic increase in assembly size over time, while light microscopy indicates liquid-liquid-phase separation (LLPS) as evidenced by the formation of micron-scale liquid droplets. Solution nuclear magnetic resonance (NMR) shows that the structural state in classical and biomimetic dopes displays a general random coil conformation in both cases; however, some subtle but distinct differences are observed, including a more ordered state for the biomimetic dope and small chemical shift perturbations indicating differences in hydrogen bonding of the protein in the different dopes with notable changes occurring for Tyr residues. Solid-state NMR demonstrates that the final wet-spun fibers from the two dopes display no structural differences of the poly(Ala) stretches, but biomimetic fibers display a significant difference in Tyr ring packing in non-β-sheet, disordered helical domains that can be traced back to differences in dope preparations. It is concluded that phosphate pre-orders the recombinant silk protein in biomimetic dopes resulting in LLPS and fibers that exhibit vastly improved toughness that could be due to aromatic ring packing differences in non-β-sheet domains that contain Tyr.

The white-rot fungus, Phanerochaete chrysosporium, under combinatorial stress produces variable oil profiles following analysis of secondary metabolites

AIMS

The effects of combinatorial stress on lipid production in Phanerochaete chrysosporium remain understudied. This species of white-rot fungi was cultivated on solid-state media while under variable levels of known abiotic and biotic stressors to establish the effect upon fungal oil profiles.

METHODS AND RESULTS

Environmental stressors induced upon the fungus included the following: temperature, nutrient limitation and interspecies competition to assess impact upon oil profiles. Fatty acid type and its concentration were determined using analytical methods of gas chromatography and mass spectrometry. Growth rate under stress was established using high-performance liquid chromatography with ergosterol as the biomarker. Fungi grown on solid-state agar were able to simultaneously produce short- and long-chain fatty acids which appeared to be influenced by nutritional composition as well as temperature. Addition of nitrogen supplements increased the growth rate, but lipid dynamics remained unchanged. Introducing competition-induced stress had significantly altered the production of certain fatty acids beyond that of the monoculture while under nutrient-limiting conditions. Linoleic acid concentrations, for example, increased from an average of 885 ng μl^-1 at monoculture towards 13 820 ng μl^-1 at co-culture, following 7 days of incubation.

CONCLUSIONS

Interspecies competition produced the most notable impact on lipid production for solid-state media cultivated fungi while the addition of nitrogen supplementation presented growth and lipid accumulation to be uncorrelated. Combinatorial stress therefore influences the yield of overall lipid production as well as the number of intermediate fatty acids produced, deriving similar oil profiles to the composition of vegetable and fish oils.

SIGNIFICANCE AND IMPACT OF THE STUDY

Fungal secondary metabolism remains highly sensitive following combinatorial stress. The outcome impacts the research towards optimizing fungal oil profiles for biomass and nutrition. Future investigations on fungal stress tolerance mechanisms need to address these environmental factors throughout the experimental design.

Towards waterjet dissection in neurosurgery: experimental in-vivo results with two different nozzle types

Waterjet dissection is under close investigation as a new neurosurgical tool. Experimentally, a precise tissue dissection with vessel preservation has been demonstrated in the porcine cadaver brain. The safety of the device has been shown in first clinical applications. However, a detailed in-vivo analysis of the waterjet device is still awaited. In the present study, two often applied nozzle types (100 microm diameter emitting a coherent straight jet; 120 microm diameter emitting a helically rotating jet) were experimentally studied in vivo. Forty-one rabbits received a frontal waterjet corticotomy on either side with one nozzle type after microsurgical removal of the arachnoid membranes. Animals were sacrificed at 1, 3, 7 days and 6 weeks after surgery. Dissection morphology and vessel preservation were evaluated. Tissue trauma was analyzed by the extent of intra-operative haemorrhage, postsurgical oedema formation and astrocytic as well as microglial reactions. In all animals, reliable brain dissection was observed. Macroscopically, only minor bleeding occurred. Microscopically, also very precise brain dissection with both nozzle types was found. Vessels were preserved with both pressures applied (5 and 10 bar). Dissections with the 100 microm straight nozzle were more precise with respect to dissection margins. However, no significant difference in vessel preservation and extent of haemorrhage, oedema formation, astrocytic and microglial reactivity was shown. Malfunction defined as clotting of the instrument occurred only with the 100 microm nozzle. In four 100 microm straight nozzle hemispheres, even no brain dissection was seen. The results indicate that the waterjet enables very precise and reliable brain parenchyma dissection with minimal trauma and vessel preservation in vivo. If this can be proven to be of clinical relevance, the instrument will become a valuable neurosurgical tool. Based on these results, the authors selected the 120 microm Helix nozzle for further research with this device in the CNS.

The diagnosis and treatment of central giant cell granuloma

This report reviews the literature involving the central giant cell granuloma. Diagnosis and treatment is presented. The article reports the case of a child who was initially seen in her general dentist's office, then referred to an oral and maxillofacial surgeon. Differential diagnoses of both benign and malignant lesions related to the central giant cell tumor are discussed.

Hypokalemic periodic paralysis: two case reports

We report two cases of hypokalemic periodic paralysis in children presenting to the emergency department with diffuse weakness and no antecedent history of neurologic disease. The literature is briefly reviewed. Any child with acute weakness and normal mental status should undergo serum potassium determination to allow prompt diagnosis and therapy.