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WIREs Nanomed Nanobiotechnol
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Engineering structure and function using thermoresponsive biopolymers

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Self‐assembly enables exquisite control at the smallest scale and generates order among macromolecular‐building blocks that remain too small to be manipulated individually. Environmental cues, such as heating, can trigger the organization of these materials from individual molecules to multipartixcle assemblies with a variety of compositions and functions. Synthetic as well as biological polymers have been engineered for these purposes; however, biological strategies can offer unparalleled control over the composition of these macromolecular‐building blocks. Biologic polymers are macromolecules composed of monomeric units that can be precisely tailored at the genetic level; furthermore, they can often utilize endogenous biodegradation pathways, which may enhance their potential clinical applications. DNA (nucleotides), polysaccharides (carbohydrates), and proteins (amino acids) have all been engineered to self‐assemble into nanostructures in response to a change in temperature. This focus article reviews the growing body of literature exploring temperature‐dependent nano‐assembly of these biological macromolecules, summarizes some of their physical properties, and discusses future directions. WIREs Nanomed Nanobiotechnol 2015, 8:123–138. doi: 10.1002/wnan.1350 This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Peptide-Based Structures
Biological polymers represent a rich source for the engineering of nanostructures. Three classes of biopolymers are evaluated within this review: DNA oligonucleotides, polysaccharides, and protein‐based sequences. Each has the ability to specifically self‐associate, which can modulate the formation of a wide variety of nanostructures. As their association depends on kinetics and/or thermodynamics, these structures are responsive to temperature. All produced from biological sources, they can be engineered by manipulation at the genetic level to varying degrees. The exquisite control exerted by biological synthetic pathways suggests that they are excellent candidates to engineer useful biomaterials.
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Resilin: a genetically engineered protein responsive to multiple stimuli. Cryo‐TEM micrographs of rec1‐resilin for solutions of (a) vitrified rec1‐resilin at 20°C has only dispersed spherical particles approximately 9.5 nm in diameter with poor contrast, which is consistent with soluble proteins. (b) Vitrified rec1‐resilin just below upper critical solution temperature (UCST) (4 °C), shows a high‐density network of well‐dispersed interconnected spherical particles with 5.4 nm diameters and excellent contrast. (c) Above lower critical solution temperature (LCST), large discrete spherical aggregates with a size range of 100–130 nm diameters form. (d) Increasing solution concentration to 10 mg mL−1 causes the formation of an interconnected gel particle network at the UCST.
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Intracellular assembly and function of elastin‐like polypeptide microdomains. (a) An amphiphilic elastin‐like polypeptide (ELP) (GFP‐S48I48) and an ELP monoblock (dsRED‐V96) with similar transition temperatures and molecular weight sort into separate microdomains in live cells. (b) An ELP fused with the clathrin‐light chain (V96‐CLC) is soluble at 31°C but assembles into V96‐CLC microdomains above 37°C. Red = ELP, green = the angiotensin II receptor (AngIIR) at the cellular membrane. (c) V96‐CLC microdomains sequester the machinery of clathrin‐mediated endocytosis and inhibit the internalization of AngIIR at 37 and 42°C. The V96‐CLC fusion remains soluble at 31°C and does not affect receptor internalization (**S < 0.0001). Mean ± 95% confidence interval (n = 3).
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Peptide‐based leucine zippers from GCN4 form nanoropes. Nanorope formation is temperature and cosolute dependent. (a) Phase image using tapping mode atomic force microscopy (AFM) of nanoropes formed in 1.5 M NaCl. The scale bar represents 500 nm and the z‐scale represents 25 nm. (b) Phase image of nanoropes formed in 0.75 M (NH4)2SO4 shows even longer structures than those in (a). (c and d) Circular dichroism was used to study the formation of alpha helices (−Θ222 nm for 144 μM peptide in 10 mM Tris, pH 8.0) as a function of (c) cosolute concentration at 25°C including Na2SO4 (●), (NH4)2SO4 (▲), and NaCl (♦) and glycerol (inset graph) and (d) temperature as a function of NaCl concentration, which shows that salt stabilizes the alpha helices until a higher temperature.
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Structural versatility of biomaterials generated from gellan gum polysaccharides. (a) Discs; (b) membranes; (c) fibers; (d) microparticles; (e and f) 3D lyophilized scaffolds.
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Oligonucleotide origami uses single‐stranded DNA (ssDNA) springs to engineer precision joints. Two arms composed of three bundles of double‐stranded DNA (18 helices total) were linked by a single rigid bundle (six helices) as well as an ssDNA spring. The length of the spring was modified to produce different angles. Conformational analysis was performed using TEM imaging. Typical particles and histogram distribution are presented with (a) 0, (b) 11, (c) 32, (d) 53, and (e) 74 bases in the ssDNA springs. The black lines show Gaussian fits to the data. The angles corresponding to the peak values of Gaussian fits were 56.5° (n = 154), 70.2° (n = 213), 97.9° (n = 169), 110.0° (n = 252), and 128.2° (n = 204). Bars = 20 nm.
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Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures
Biology-Inspired Nanomaterials > Peptide-Based Structures
Nanotechnology Approaches to Biology > Nanoscale Systems in Biology

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