Human insulin production was severely limited by its complex downstream processing. Herein, an insulin-imprinted polymer with shape-memorable imprint cavities was designed for the separation and ...purification of insulin from complex biofluids. N-isopropylacrylamide (NIPAM) was chosen as main monomer, and acrylamide (AAm) and (3-acrylamidopropyl)trimethylammonium chloride (AAPTAC) as functional monomers. A poly(l-lysine)-based peptide crosslinker, instead of the commonly used crosslinkers, was used to introduce poly(l-lysine) segments into the polymer. Because of the reversible and precise pH-induced helix-coil transition of the poly(l-lysine) segments, the imprint cavities in the polymer are shape-memorable. For this reason, the insulin template can be removed completely under mild conditions, meanwhile the imprinting efficiency is significantly improved. A high adsorption capacity (595 mg/g) and a high imprinting factor (5.83) were obtained, both of which are significantly higher than the previously developed insulin-imprinted polymers. The polymer also exhibits a high selectivity towards insulin and can be used repeatedly. Using this polymer insulin spiked in human serum was selectively captured and separated, demonstrating its ability for separation and purification of insulin from complex biofluids.
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•Peptide-crosslinked insulin-imprinted polymers with shape-memorable imprint cavities were designed.•The insulin template can be removed completely under mild conditions.•A high adsorption capacity and a high imprinting factor were achieved.•Insulin can be separated efficiently from complex biofluid using the polymer.
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Protein-imprinted polymers are artificial receptors capable of recognizing protein. They are highly promising for applications in important bio-related areas, however, their ...development was severely retarded by two problems: difficult template removal and low imprinting efficiency. The two problems could be overcome by constructing shape-memorable imprinted cavities using peptide crosslinker. Here a new oligo-l-lysine-based peptide crosslinker was designed and synthesized. A novel cytochrome c (Cyt C)-imprinted polymer was synthesized using the new peptide crosslinker. When switching pH between 12 and 7.4, the peptide segments incorporated in the polymer underwent reversible helix-coil transition. Because of the precise folding of the peptide segments, the imprinted cavities in the polymer could be enlarged when lowering pH to 7.4 to release the template protein, but restore their original size and shape at pH 12 to recognize the template protein. Therefore complete template removal was achieved under mild conditions. Meanwhile the imprinting efficiency was improved significantly. Compared to polymer crosslinked with the commonly used crosslinker N, N-methylenebisacrylamide, the imprinting efficiency of the peptide-crosslinked polymer was increased by 15 times. The new imprinted polymer presented not only a high adsorption capacity (454.4 mgg−1), a high imprinting factor (6.3), high selectivity towards Cyt C, and excellent reusability, but also could preserve the fragile secondary structure of the eluted protein, and therefore had high potential in bioseparation. As a demonstration, Cyt C added into fetal bovine serum was separated from the sample using the polymer via a simple adsorption-desorption cycle. The recovery rate was as high as 92.7%.
•Helix-specific properties and applications of polypeptides were summarized.•Structural features of α-helices were highlighted.•Future directions on the studies of polypeptide conformation were ...discussed.
Polypeptides obtained from the ring-opening polymerization of N-carboxyanhydrides, as the synthetic analogues of natural proteins, have drawn broad interests during the recent three decades. Unlike other synthetic polymers, polypeptides form ordered secondary structures like α-helices and β-sheets, which offer conformation-specific functions that are not observed in unstructured polymers. In this article, we summarized the unique structural features of α-helical polypeptides compared to their random-coiled analogues, and reviewed the helix-associated assembly behaviors and biomedical functions based on the structural differences. In addition, the characterization and modulation of polypeptide conformations were also discussed. We believe this review will shed light on the future design of synthetic polypeptides with helix-specific properties, further expanding the scope of polypeptide materials.
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► The helical stability of poly-glutamic acid is sensitive to temperature and pH. ► Helix–coil dynamics were studied using nanosecond temperature jumps and IR detection. ► Dynamics ...are non-exponential, indicating the multi-step nature of the process. ► Dynamics are slowest near the mid-point of the pH-induced helix–coil transition. ► This agrees with theoretical predictions for cooperative transitions in polymers.
Poly-L-glutamic acid (PGA) is an ideal model system for investigating the transition between α-helical and random coil peptide conformations, since its secondary structure is highly sensitive not only to temperature, but also to pH. Laser pulse-induced temperature jumps were used to observe pH-dependent PGA helix–coil relaxation dynamics on the microsecond time scale. The relaxation was found to be non-exponential, particularly if only short helical segments are present before the temperature jump, indicating the multi-step nature of the process which involves helix nucleation and propagation. Helix–coil relaxation is slowest near the mid-point of the pH-induced helix–coil transition, in agreement with theoretical predictions.
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•PPy/Ca-alginate/Gel microsphere contained temperature-sensitive gelatin and sunlight-sensitive PPy.•PPy can convert the absorbed light into heat energy and cause the structural ...transition of gelatin.•Helix-coil structure transition of gelatin could promote the release of carbendazim.•PPy/Ca-alginate/Gel has great potential in agriculture for agrochemicals release.
Responsive controlled-release systems can not only improve the efficiency of agrochemical utilization but also increase crop yield and reduce environmental pollution caused by excessive use of agrochemicals. In this paper, the helix-coil structural transition of gelatin was adopted to construct a novel stimuli-responsive controlled-release system called polypyrrole/Ca-alginate/gelatin (PPy/Ca-alginate/Gel). In PPy/Ca-alginate/Gel, Ca-alginate and gelatin form a semi-interpenetrating network in which uncross-linked gelatin can undergo a free helix-coil structural transition due to the photothermal effect of PPy. The structural transition of gelatin will lead to changes in the functional groups and microstructure of semi-interpenetrating hydrogels and furthermore achieve the release of template agrochemical molecules embedded in hydrogels. By using carbendazim as a template molecule, the photothermal conversion and controlled release of PPy/Ca-alginate/Gel were systematically studied. After 600 s of light irradiation, its temperature could be increased by 17 ℃. The release of carbendazim in microspheres reached 91.8 % after 8 h of light irradiation, while it was only 13.3 % in the dark. The results indicated that PPy/Ca-alginate/Gel have excellent controlled-release and sustained-release properties and broad application potential in agriculture.
•Aggregation network varied in both degree and type with gelling temperature.•Lower temperatures created a stronger and crumbly gel.•Stronger gels corresponded to a network of greater enthalpy and ...entropy.•Bonds showed partial thermal irreversibility.
Gelation of maltodextrin (DE 2) was examined over a range of temperatures to understand the behaviour within mixed-gel systems. Maltodextrin solutions were prepared at 95 °C and held at temperatures between 5 °C and 60 °C for four days. Bulk gel properties and the underlying microstructure were analysed using fracture strength, proton relaxation time, and differential scanning calorimetry (DSC). Holding at lower temperatures led to a greater gel strength with a brittle and crumbly texture. Analysis of the microstructure showed that gelation at 10 °C versus 60 °C produced a greater number of aggregates (melting enthalpy 14.5 J/g versus 3.4 J/g) and structuring of a higher melting entropy (45 mJ/g K versus 10 mJ/g K). A thermal hysteresis with signs of structure corresponding to both holding temperatures was also measured. Elevated temperature was hypothesized to decrease the amount of smaller molecular weight chains participating in aggregation by shifting from the helix to coil form.
Depletion of human serum albumin (HSA), the most abundant protein in human plasma, from serum/plasma is a prerequisite before their proteomic analysis. Molecularly imprinted polymers (MIPs) using HSA ...as a template have been designed for this purpose, but suffer from a low sorption capacity and low selectivity. Here, a new HSA-imprinted polymer was synthesized using N-isopropylacrylamide (NIPAM) as the main monomer; acrylamide (AAm), methacrylic acid (MAA), and dimethylaminoethyl methacrylate (DMAEMA) as functional monomers; and oligoglutamic acid-based peptide crosslinker (PC) as a crosslinker at pH 5.5. When pH is adjusted to 7.4, the peptide chains in the polymer change from a helical conformation to an extended coil conformation, and the polymer swells. Consequently, the template protein is removed completely. When pH is adjusted back to 5.5, the peptide chains fold back precisely to the helical conformation. Both the size and shape of the imprint cavities are restored. Therefore, the polymer rebinds the template protein selectively. Highest imprinting factor (IF) was observed at pH 5.5 at which the polymer was synthesized. The IF increases with the increasing number of glutamic acid residues in the PCs because of their increased degree of helicity at pH 5.5. No improvement in imprinting effect was observed when using a peptide crosslinker containing both L- and D-glutamic acid residues and hence incapable of folding into α-helix, further confirming the key role of the pH-induced helix-coil transition of the peptide chains. The MIP synthesized here presents a much higher affinity to HSA than the nontemplate proteins. It could be used repeatedly without evident decrease in sorption capacity. Because of the mild eluting conditions, the secondary structure of the extracted HSA protein remains unchanged. Finally, the MIP was used to deplete HSA from human serum. Because of its high sorption capacity and high selectivity, HSA was depleted completely and selectively.
A new molecularly imprinted polymer (MIP) using human serum albumin (HSA) as a template was synthesized using N-isopropylacrylamide (NIPAM) as the main monomer; acrylamide (AAm), methacrylic acid (MAA), and dimethylaminoethyl methacrylate (DMAEMA) as functional monomers; and oligoglutamic acid-based peptide crosslinker as a crosslinker. Because of the reversible and precise pH-induced helix-coil transition of the peptide chains, the template protein was removed facilely and completely under mild conditions. Simultaneously, a significant improvement in imprinting efficiency was obtained. The sorption capacity was as high as 648.05 mg/g and the imprinting factor was 7.9. Because of its high selectivity and high binding capacity, the MIP synthesized here is highly promising for the depletion of HSA, the most abundant protein in serum, which is a prerequisite for its proteomic analysis. For the first time, complete and selective depletion of HSA from human serum was achieved using a protein-imprinted polymer.
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Self-assembly behavior of poly(γ-benzyl l-glutamate)-graft-poly(ethylene glycol) (PBLG-g-PEG) in ethanol medium was studied by transmission electron microscopy (TEM), scanning electron microscopy ...(SEM), laser light scattering (LLS), and circular dichroism (CD). The experimental results revealed that the conformation change of the polypeptide graft copolymer exerts marked effect on its self-association behavior. Spindle-like micelles with polypeptide blocks aligned inside the cores are formed in ethanol solution without denaturant acid. When the denaturant acid is added, the rigid α-helix transforms to random coil, resulting in an aggregate structure change from the spindle-like micelle to large compound micelle. For the large compound micelles, the coiled polypeptide chains and PEG blocks pack randomly within the cores, surrounded by the PEG chains outside to stabilize the aggregates.
A simple model is introduced to describe re-entrant isotropic-nematic and nematic-smectic A phase transitions mediated helix-coil transition and solvation within individual liquid crystalline ...semiflexible polymers in a solution. We consider hydrogen bonding between the polymer and solvent molecules (solvation) as an intermolecular interaction and helix-coil transformations of the polymer as an intramolecular interaction. The helix part is rigid and can form nematic and smectic A phases. On the other hand, the solvation prevents liquid crystalline ordering of the polymer chains. At high temperatures, a polymer is in a coiled state without solvation. With decreasing temperatures, solvation and helix-coil transitions compete in the individual semiflexible polymers, and the re-entrant phase transitions occur. We also discuss the chain conformation by calculating Kuhn length.
The conformational equilibrium between 310‐ and α‐helical structure has been studied via high‐resolution NMR spectroscopy by Millhauser and coworkers using the MW peptide Ac‐AMAAKAWAAKA AAARA‐NH2. ...Their 750‐MHz nuclear Overhauser effect spectroscopy (NOESY) spectra were interpreted to reflect appreciable populations of 310‐helix throughout the peptide, with the greatest contribution at the N and C termini. The presence of simultaneous αN(i,i + 2) and αN(i,i + 4) NOE cross‐peaks was proposed to represent conformational averaging between 310‐ and α‐helical structures. In this study, we describe 25‐nsec molecular dynamics simulations of the MW peptide at 298 K, using both an 8 Å and a 10 Å force‐shifted nonbonded cutoff. The ensemble averages of both simulations are in reasonable agreement with the experimental helical content from circular dichroism (CD), the 3JHNα coupling constants, and the 57 observed NOEs. Analysis of the structures from both simulations revealed very little formation of contiguous i → i + 3 hydrogen bonds (310‐helix); however, there was a large population of bifurcated i → i + 3 and i → i + 4 α‐helical hydrogen bonds. In addition, both simulations contained considerable populations of π‐helix (i → i + 5 hydrogen bonds). Individual turns formed over residues 1–9, which we predict contribute to the intensities of the experimentally observed αN(i,i + 2) NOEs. Here we show how sampling of both folded and unfolded structures can provide a structural framework for deconvolution of the conformational contributions to experimental ensemble averages.
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