Spontaneous Alignment of Self‐Assembled Cationic and Amphiphilic β‐Sheet Peptides

Abstract

Aligned peptide assemblies are of interest for both fundamental understanding of biological systems as well as development of novel biomaterials. Herein, Pro‐Lys‐(Phe‐Lys)5‐Pro (PFK), a cationic and amphiphilic β‐sheet synthetic peptide that self‐assembles into fibrils, capable of undergoing spontaneous isotropic to nematic phase transition, that intrinsically aligns in solution, is presented. Upon dissolution PFK forms isotropically dispersed fibrils due to delicate balance between attractive H bonds and hydrophobic interactions to electrostatic repulsive forces. The transition from isotropic to nematic phase alignment occurring over a period of several days is monitored in situ by both small‐angle X‐ray scattering and cryogenic transmission electron microscopy. The degree of alignment and the time required to achieve a complete isotropic–nematic phase transition of PFK fibrils in aqueous solution is found to be concentration dependent as predicted by Onsager's excluded volume theory. Remarkably, PFK nematic phases remain aligned over the course of several months without the application of any external stimuli. Aligned PFK gels can be formed by mild shearing through a salty medium. This system provides a novel route for producing nanoscale aligned materials for potential biomedical applications.

Hierarchical Membranes Self‐Assembled at the Interface between Peptides and Polymer Aqueous Solutions

“…An AP that doesn't comply with this assumption is the cationic and amphiphilic β-sheet peptide PK(FK) 5 P (PFK), which was shown by Cryo-TEM to self-assemble into short fibrils that elongate over days and organize into an aligned pattern, without any external stimuli, as was confirmed by the characteristic bow-tie shape of its SAXS 2D scan, and thus assumed to be in a thermodynamically metastable state. [30] Membranes produced by combining PFK with negatively charged alginate, i. e., alginate/PFK membranes, exhibited a three-region morphology. However, while for PA membranes, the region of the perpendicular fibers formed rapidly (i. e., in a minute time scale), in PFK membranes, it developed over days, allowing to carefully monitor the membrane evolution.…”

“…An underlying assumption regarding all the PAs and APs described thus far is that their self‐assembled aggregates are either stable in a thermodynamic equilibrium or a kinetically trapped state prior to the membrane formation. An AP that doesn't comply with this assumption is the cationic and amphiphilic β‐sheet peptide PK(FK) 5 P (PFK), which was shown by Cryo‐TEM to self‐assemble into short fibrils that elongate over days and organize into an aligned pattern, without any external stimuli, as was confirmed by the characteristic bow‐tie shape of its SAXS 2D scan, and thus assumed to be in a thermodynamically metastable state [30] …”

Macroscopic membranes self‐assembled by alginate and a cationic and amphiphilic peptide for cell culture

“…Only a few examples of such membranes were produced with non‐lipidated amphiphilic peptides (e.g., FF, K 2 X n F 4 , K 2 (QL) 6 K 2 ) and these were also shown to support cells growth 9,10,13 . In the majority of the membranes developed to support cell growth, a specific bioactive epitope (e.g., RGD) was incorporated in the peptide sequence.Based on the principles described above, we recently developed new macroscopic planar and spherical membranes, 12 combining the negatively charged biopolymer, alginate, with the cationic and amphiphilic peptide Pro‐Lys‐(Phe‐Lys) 5 ‐Pro, denoted PFK 19–21 . This peptide presents the general sequence Pro‐X‐(Phe‐X) 5 ‐Pro, in which X is a charged amino acid, alternating with the hydrophobic Phe amino acid along the backbone.…”

“…[20][21][22][23][24][25][26] Alginate/PFK membranes were formed by a three-step mechanism. At a sufficiently high concentration (5% w/v) PFK forms β-sheet soluble assemblies that behave analogously to polyelectrolyte chains, 19 and these form with an alginate (2% w/v) solution, the condensed-layer 12 (1st step). Rearrangements in this layer, which take place over days, result in a semi-permeable membrane (2nd step) through which PFK fibrils are unable to diffuse but through which alginate reptate once difference in osmotic pressure reaches a critical point (3rd step).…”

“…12 Here we set to study the alginate/PFK membranes' suitability for cell culture applications. Of note, both components may pose challenges to cell culture; Alginate, which is considered nontoxic, lacks biological cues that are essential for cell adhesion, 27 and PFK, which assembles into positively charged fibrils, 19 may impart cytotoxicity. 21,28 Planar membranes and spherical membranes were generated and then incubated for 1 day (denoted fresh-membranes) or 6 days (denoted aged-membranes).…”