María’s comment on: Artificially Engineered Protein Hydrogels Adapted from the Nucleoporin Nsp1 for Selective Biomolecular Transport

Maria Luisa Adrover


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The main goal of the article by the Olsen group is to present a new protein hydrogel composed of nucleoporin like polypeptides that allow a selective transport of biomolecules into the formed hydrogel. The engineering of this system was inspired by the selectivity of the protein matrix in the nuclear pore complex. The nuclear pore complex is composed of nucleoporins like Nsp1 (16 repeats of a 19 amino acid sequence). These are proteins containing Phe-Gly (FG) repeats that contribute to specific binding of the nuclear transport receptors. The authors took advantage of the finding that individual nucleoporins can form hydrogels in vitro. They designed three different nucleoporin-like polypeptides (NLP) using pentameric (P) coiled-coil domains in the C and N terminus of the polypeptide: P-1NLP-P, P-2NLP-P and P-cNsp1-P (the original nucleoporin).

In their experiments, they conducted rheology studies (using oscillations as a type stress) to evaluate the flow properties of the protein hydrogel. They found that the hydrogel in behaves in some cases as a viscous liquid (when G“ > G`) while in other cases it behaves as an elastic solid (when G` > G“). Also, they noticed by adding hexanediol, the FG repeats were weakened making the hydrogel less elastic. Another study was done using Raman spectroscopy too see any changes in the peaks of the spectra. They saw that by adding hexanediol there was a reduction the Phe vibrational mode of 486 cm-1 meaning that the FG repeats where indeed being disrupted. Lastly, using capillary experiments they studied the selective transport of the protein hydrogels. They studied the selectivity of the biomolecules measuring the fluorescence intensity of: Importin β, IBB-MBP-EGFP (Importin β binding with maltose binding protein and enhanced green fluorescent protein) and MBP-mCherry. Fluorescence studies showed that Importin β was diffused inside P-cNsp1-P hydrogel with the highest intensity, followed by P-2NLP-P and lastly P-1NLP-P. Interestingly, they showed that just by changing one amino acid (Serine to Aspartic Acid) the selectivity for Importin β changed. This suggested that small changes to the nucleoporin like polypeptides affects the selectivity. Adding 10% hexanediol to P-2NLP-P barely showed fluorescence mainly due to the FG disruptions mentioned before. Finally, a successful engineering of hydrogels was achieved showing a high selectivity just like the natural nucleoporin system. A relatively simple polypeptide chain just like the cNsp1 allow the design of nucleoporin-like polypeptides as selective as the protein matrix found inside the nuclear pore complex.

José’s comment on: Intelligent, Biodegradable, and Self-Healing Hydrogels Utilizing DNA Quadruplexes

By José M. Martinez

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This paper is about making of a water based gel made from the supramolecular interactions of guanosine rich oligonucleotides. They attached these oligonucleotides symmetrically into the ends of PEG chains of variable lengths and conformations. This was made through High Efficiency Liquid Phase (HELP) synthesis. This synthetic strategy, as its name says, occurs in a liquid phase instead of the usual solid phase synthesis. The purpose of this is to allow them to obtain greater quantities of product more easily without risking the effectiveness. These DNA-PEG-DNA monomers have the ability, when diluted and presented with a cation (K+ or Na+), to self-assemble its DNA moieties through non-covalent interactions to for G-quadruplexes. Those strong interactions change the physical properties of the solution by forming a hydrogel. In the study, it was proven that the concentration of the cation required to trigger the self-assembly is relatively small. It is even compared to the concentration of salts found in body-related fluids like sweat, saliva, and tears. The hydrogel also has the capability to heal itself and interact by diffusion with another of the same kind. Finally, it was found that by adding a few extra nucleotides to the DNA moiety of the monomer and a matching strand for that part, the G-quadruplexes could be disassembled, returning the gel back to its liquid phase. All the previously stated properties indicate potential uses of this hydrogel for biomedical purposes.
Regarding myself, I learned mostly about the molecular aspect of gels and how they are formed. It was very interesting seeing the role that the supramolecular interactions played in the formation of this particular gel and the experiments made to investigate further into its properties.

JMM: Tanaka, 2017. Intelligent, Biodegradable, and Self-Healing Hydrogels Utilizing DNA Quadruplexes