Maria Luisa Adrover
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.