Enzymes fold into unique three-dimensional structures, which underlie their remarkable catalytic properties. The requirement to adopt a stable, folded conformation is likely to contribute to their relatively large size (> 10,000 Dalton). However, much shorter peptides can achieve well-defined conformations through the formation of amyloid fibrils. To test whether short amyloid-forming peptides might in fact be capable of enzyme-like catalysis, we designed a series of 7-residue peptides that act as Zn2+-dependent esterases. Zn2+ helps stabilize the fibril formation, while also acting as a cofactor to catalyze acyl ester hydrolysis. These results indicate that prion-like fibrils are able to not only catalyze their own formation – they also can catalyze chemical reactions. Thus, they might have served as intermediates in the evolution of modern-day enzymes. These results also have implications for the design of self-assembling nanostructured catalysts including ones containing a variety of biological and nonbiological metal ions.
The brown color of Arabidopsis seeds is caused by the deposition of proanthocyanidins (PAs or condensed tannins) in their inner testa layer. A transcription factor complex consisting of TT2, TT8 and TTG1 controls expression of PA biosynthetic genes, just as similar TTG1-dependent complexes have been shown to control flavonoid pigment pathway gene expression in general. However, PA synthesis is controlled by at least one other gene. TTG2 mutants lack the pigmentation found in wild-type seeds, but produce other flavonoid compounds, such as anthocyanins in the shoot, suggesting that TTG2 regulates genes in the PA biosynthetic branch of the flavonoid pathway. We analyzed the expression of PA biosynthetic genes within the developing seeds of ttg2-1 and wild-type plants for potential TTG2 regulatory targets. We found that expression of TT12, encoding a MATE type transporter, is dependent on TTG2 and that TTG2 can bind to the upstream regulatory region of TT12 suggesting that TTG2 directly regulates TT12. Ectopic expression of TT12 in ttg2-1 plants partially restores seed coat pigmentation. Moreover, we show that TTG2 regulation of TT12 is dependent on TTG1 and that TTG1 and TTG2 physically interact. The observation that TTG1 interacts with TTG2, a WRKY type transcription factor, proposes the existence of a novel TTG1-containing complex, and an addendum to the existing paradigm of flavonoid pathway regulation.
Complete crush- or cut- severance of sciatic nerve axons in rats and other mammals produces immediate loss of axonal continuity. Loss of locomotor functions subserved by those axons are not restored for months, if ever, by outgrowths regenerating at ~1 mm/d from the proximal stumps of severed axonal segments. The distal stump of a severed axon typically begins to degenerate in 1–3 days. We have recently developed a PEG-fusion technology consisting of sequential exposure of severed axonal ends to hypotonic Ca2+-free saline, methylene blue (MB), polyethylene glycol (PEG) in distilled water, and finally to Ca2+-containing isotonic saline. We examined factors that affect the PEG-fusion restoration of axonal continuity within minutes as measured by conduction of action potentials and diffusion of an intracellular fluorescent dye across the lesion site of rat sciatic nerves completely cut- or crush-severed in the mid-thigh. We also examined factors that affect the longer-term PEG-fusion restoration of lost behavioral functions within days to weeks as measured by the Sciatic Functional Index. We report that exposure of cut-severed axonal ends to Ca2+-containing saline prior to PEG-fusion and stretch/tension of proximal or distal axonal segments of cut-severed axons decrease PEG-fusion success. Conversely, trimming cut-severed ends in Ca2+-free saline just prior to PEG-fusion increases PEG-fusion success. PEG-fusion prevents or retards the Wallerian degeneration of cut-severed axons as assessed by measures of axon diameter and G ratio. PEG-fusion may produce a paradigm-shift in the treatment of peripheral nerve injuries.
Background:Nervous system injuries in mammals often involve transection or segmental loss of peripheral nerves. Such injuries result in functional (behavioral) deficits poorly restored by naturally occurring 1-2mm/d axonal outgrowths aided by primary repair or reconstruction. "Neurorrhaphy" or nerve repair joins severed connective tissues, but not severed cytoplasmic/ plasmalemmal extensions (axons) within the tissue.New Method: PEG-fusion consists of neurorrhaphy combined with a well-defined sequence of four pharmaceutical agents in solution, one containing polyethylene glycol (PEG), applied directly to closely apposed viable ends of severed axons.Results: PEG-fusion of rat sciatic nerves: (1) restores axonal continuity across coaptation site(s) within minutes, (2) prevents Wallerian degeneration of many distal severed axons, (3) preserves neuromuscular junctions, (4) prevents target muscle atrophy, (5) produces rapid and improved recovery of voluntary behaviors compared with neurorrhaphy alone, and (6) PEG-fused allografts are not rejected, despite no tissue-matching nor immunosuppression.Comparison with existing methods: If PEG-fusion protocols are not correctly executed, the results are similar to that of neurorrhaphy alone: (1) axonal continuity across coaptation site(s) is not re-established, (2) Wallerian degeneration of all distal severed axons rapidly occurs, (3) neuromuscular junctions are non-functional, (4) target muscle atrophy begins within weeks, (5) recovery of voluntary behavior occurs, if ever, after months to levels well-below that observed in unoperated animals, and (6) allografts are either rejected or not well-accepted.Conclusion: PEG-fusion produces rapid and dramatic recovery of function following rat peripheral nerve injuries.
Nanotechnology creates materials that potentially outperform, at several boundaries, existing materials in terms of mechanical, electrical, catalytic, and optical properties. However, despite their promise to mimic the surface roughness cells experience in vivo, the use of nanophase materials in biological applications remains to date largely unexplored. The objective of the present in vitro study was, therefore, to determine whether when added to a polymer scaffold, nanophase compared to conventional ceramics enhance functions of osteoblasts (or bone-forming cells). Results from this study provided the first evidence that functions (specifically, adhesion, synthesis of alkaline phosphatase, and deposition of calcium-containing mineral) of osteoblasts increased on poly-lactic-co-glycolic acid (PLGA) scaffolds containing nanophase compared to conventional grain size titania with greater weight percentage (from 10-30 wt %). Because the chemistry, material phase, porosity (%), and pore size of the composites were similar, this study implies that the surface features created by adding nanophase compared to conventional titania was a key parameter that enhanced functions of osteoblasts. In this manner, the study adds another novel property of nanophase ceramics: their ability to promote osteoblast functions in vitro when added to a polymer scaffold. For this reason, nanophase ceramics (and nanomaterials in general) deserve further attention as orthopedic tissue engineering materials.
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