Thermal stress, p53 structures and learning from elephants.

As species adapt to climatic changes, temperature-dependent functions of p53 in development, metabolism and cancer will adapt as well. Structural analyses of p53 epitopes interacting in response to environmental stressors, such as heat, may uncover physiologically relevant functions of p53 in cell regulation and genomic adaptations. Here we explore the multiple p53 elephant paradigm with an experimentally validated in silico model showing that under heat stress some p53 copies escape negative regulation by the MDM2 E3 ubiquitin ligase. Multiple p53 isoforms have evolved naturally in the elephant thus presenting a unique experimental system to study the scope of p53 functions and the contribution of environmental stressors to DNA damage. We assert that fundamental insights derived from studies of a historically heat-challenged mammal will provide important insights directly relevant to human biology in the light of climate change when 'heat' may introduce novel challenges to our bodies and health.

Uncoupling elephant TP53 and cancer.

Elephant testicles do not descend, with implications for sperm production being hot enough to compromise germline DNA replication/repair. Uniquely, elephants also possess 20 copies of a gene encoding for the p53 protein. Did elephants evolve multiplication of the TP53 gene complex to protect their germline rather than to fight cancer?

The Elephant Evolved p53 Isoforms that Escape MDM2-Mediated Repression and Cancer.

The p53 tumor suppressor is a transcription factor with roles in cell development, apoptosis, oncogenesis, aging, and homeostasis in response to stresses and infections. p53 is tightly regulated by the MDM2 E3 ubiquitin ligase. The p53-MDM2 pathway has coevolved, with MDM2 remaining largely conserved, whereas the TP53 gene morphed into various isoforms. Studies on prevertebrate ancestral homologs revealed the transition from an environmentally induced mechanism activating p53 to a tightly regulated system involving cell signaling. The evolution of this mechanism depends on structural changes in the interacting protein motifs. Elephants such as Loxodonta africana constitute ideal models to investigate this coevolution as they are large and long-living as well as having 20 copies of TP53 isoformic sequences expressing a variety of BOX-I MDM2-binding motifs. Collectively, these isoforms would enhance sensitivity to cellular stresses, such as DNA damage, presumably accounting for strong cancer defenses and other adaptations favoring healthy aging. Here we investigate the molecular evolution of the p53-MDM2 system by combining in silico modeling and in vitro assays to explore structural and functional aspects of p53 isoforms retaining the MDM2 interaction, whereas forming distinct pools of cell signaling. The methodology used demonstrates, for the first time that in silico docking simulations can be used to explore functional aspects of elephant p53 isoforms. Our observations elucidate structural and mechanistic aspects of p53 regulation, facilitate understanding of complex cell signaling, and suggest testable hypotheses of p53 evolution referencing Peto's Paradox.

Identification and classification of silks using infrared spectroscopy.

Lepidopteran silks number in the thousands and display a vast diversity of structures, properties and industrial potential. To map this remarkable biochemical diversity, we present an identification and screening method based on the infrared spectra of native silk feedstock and cocoons. Multivariate analysis of over 1214 infrared spectra obtained from 35 species allowed us to group silks into distinct hierarchies and a classification that agrees well with current phylogenetic data and taxonomies. This approach also provides information on the relative content of sericin, calcium oxalate, phenolic compounds, poly-alanine and poly(alanine-glycine) ß-sheets. It emerged that the domesticated mulberry silkmoth Bombyx mori represents an outlier compared with other silkmoth taxa in terms of spectral properties. Interestingly, Epiphora bauhiniae was found to contain the highest amount of ß-sheets reported to date for any wild silkmoth. We conclude that our approach provides a new route to determine cocoon chemical composition and in turn a novel, biological as well as material, classification of silks.

Tensile and shear mechanical properties of rotator cuff repair patches.

BACKGROUND: Augmentation of rotator cuff tears aims to strengthen the repair and reduce rerupture, yet studies still report high failure rates. This study determines key mechanical properties of rotator cuff repair patches, including establishing values for toughness and measuring the shear properties of repair patches and human rotator cuff tendons. We hypothesized that different repair grafts would (1) have varying material parameters, and (2) not all have mechanical properties similar to human rotator cuff tendons. MATERIALS AND METHODS: Eight specimens each from the Restore, GraftJacket, Zimmer Collagen Repair, and SportsMesh repair patches were tested to failure in tension and for suture pullout. We assessed ultimate tensile strength, tensile (Young's) modulus, and failure strain. This study also established toughness values and shear data. Storage modulus was calculated using dynamic shear analysis for the patches and 18 samples of normal rotator cuff tendon. RESULTS: We report significant variability in important mechanical properties of repair patches, with the mechanical parameters of the patches diverting variously-and often significantly-from values for human rotator cuff tendon. CONCLUSIONS: The repair grafts tested all displayed significant variation in their mechanical properties and had at least some reduced parameters compared with human rotator cuff tendons. This study offers experimentally derived information of value to surgeons when selecting rotator cuff repair grafts. A better understanding of the mechanical suitability of repair grafts for supporting human rotator cuffs is needed if repair patches are to provide a solution for the clinical problem of failure of rotator cuff repairs.

Breaking the 200 nm limit for routine flow linear dichroism measurements using UV synchrotron radiation.

The first synchrotron radiation flow linear dichroism spectra are reported. High-quality spectral data can be collected from 450 nm down to 180 nm in contrast to the practical cutoff of approximately 200 nm on benchtop instruments. State-of-the-art microvolume capillary Couette flow linear dichroism was successfully ported to a synchrotron radiation source. The sample volume required is < 50 microL. A characterization of the synchrotron radiation linear dichroism with known DNA and DNA-ligand systems is presented and the viability of the setup confirmed. Typically, wavelengths down to 180 nm are now routinely accessible with a high signal/noise ratio with little limitation from the sample concentration. The 180 nm cutoff is due to the quartz of the Couette cell rather than the beamline itself. We show the application of the simultaneous determination of the sample absorption spectrum to calculate the reduced linear dichroism signal. Spectra for calf thymus DNA, DNA/ethidium bromide, and DNA/4',6-diamidino-2-phenylindole systems illustrate the quality of data that can be obtained.

Transient Expression of a Major Ampullate Spidroin 1 Gene Fragment from Euprosthenops sp. in Mammalian Cells.

Spider silk possesses extraordinary and unsurpassed mechanical properties and several attempts have been made to artificially produce spider silk in order to manufacture strong and light engineering composites. In the field of oncology, recombinant spider silk has the potential to be used as a biomaterial for bone replacement after tumour surgery. In this study, a 636-base pair gene fragment, coding for a part of major ampullate spidroin 1 from the African spider, Euprosthenops sp., was cloned into the expression vector pSecTag2/Hygro A, designed for the production of protein in mammalian cells. COS-1 cells were subsequently transfected with the recombinant plasmids and transient expression of low amounts of the corresponding silk protein fragment was obtained. The expressed fragment contained repetitive sequences associated with intrinsic biomechanical properties and has potential as a starting material for designed biopolymers.

Characterization of the protein components of Nephila clavipes dragline silk.

Spider silk is predominantly composed of structural proteins called spider fibroins or spidroins. The major ampullate silk that forms the dragline and the cobweb's frame threads of Nephila clavipes is believed to be a composite of two spidroins, designated as Masp 1 and 2. Specific antibodies indeed revealed the presence of Masp 1 and 2 specific epitopes in the spinning dope and solubilized threads. In contrast, sequencing of specific peptides obtained from solubilized threads or gland urea extracts were exclusively homologous to segments of Masp 1, suggesting that this protein is more abundantly expressed in silk than Masp 2. The strength of immunoreactivities corroborated this finding. Polypeptides reactive against both Masp 1 and 2 specific antibodies were found to be expressed in the epithelia of the tail and different gland zones and accumulated in the gland secreted material. Both extracts of gland secretion and solubilized threads showed a ladder of polypeptides in the size range of 260-320 kDa in gel electrophoresis under reducing conditions, whereas gel filtration chromatography yielded molecular masses of the proteins of approximately 300-350 kDa. In the absence of a reducing agent, dimeric forms of the spidroins were observed with estimated molecular masses of 420-480 kDa according to gel electrophoresis and 550-650 kDa as determined by gel filtration chromatography. Depending on the preparation, some silk material readily underwent degradation, and polypeptides down to 20 kDa in size and less were detectable.

Structural conformation of spidroin in solution: a synchrotron radiation circular dichroism study.

Spider silk is made and spun in a complex process that tightly controls the conversion from soluble protein to insoluble fiber. The mechanical properties of the silk fiber are modulated to suit the needs of the spider by various factors in the animal's spinning process. In the major ampullate (MA) gland, the silk proteins are secreted and stored in the lumen of the ampulla. A particular structural fold and functional activity is determined by the spidroins' amino acid sequences as well as the gland's environment. The transition from this liquid stage to the solid fiber is thought to involve the conversion of a predominantly unordered structure to a structure rich in beta-sheet as well as the extraction of water. Circular dichroism provides a quick and versatile method for examining the secondary structure of silk solutions and studying the effects of various conditions. Here we present the relatively novel technique of synchrotron radiation based circular dichroism as a tool for investigating biomolecular structures. Specifically we analyze, in a series of example studies on structural transitions induced in liquid silk, the type of information accessible from this technique and any artifacts that might arise in studying self-assembling systems.

Spinning an elastic ribbon of spider silk.

The Sicarid spider Loxosceles laeta spins broad but very thin ribbons of elastic silk that it uses to form a retreat and to capture prey. A structural investigation into this spider's silk and spinning apparatus shows that these ribbons are spun from a gland homologous to the major ampullate gland of orb web spiders. The Loxosceles gland is constructed from the same basic parts (separate transverse zones in the gland, a duct and spigot) as other spider silk glands but construction details are highly specialized. These differences are thought to relate to different ways of spinning silk in the two groups of spiders. Loxosceles uses conventional die extrusion, feeding a liquid dope (spinning solution) to the slit-like die to form a flat ribbon, while orb web spiders use an extrusion process in which the silk dope is processed in an elongated duct to produce a cylindrical thread. This is achieved by the combination of an initial internal draw down, well inside the duct, and a final draw down, after the silk has left the spigot. The spinning mechanism in Loxosceles may be more ancestral.