Transformation of Amyloid-like Fibers, Formed from an Elastin-Based Biopolymer, into a Hydrogel:  An X-ray Photoelectron Spectroscopy and Atomic Force Microscopy Study

Abstract

Previous studies have revealed the propensity of elastin-based biopolymers to form amyloid-like fibers when dissolved in water. These are of interest when considered as "ancestral units" of elastin in which they represent the simplest sequences in the hydrophobic regions of the general type XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu). We normally refer to these biopolymers based on elastin or related to elastin units as "elastin-like polypeptides". The requirement of water for the formation of amyloids seems quite interesting and deserves investigation, the water representing the natural transport medium in human cells. As a matter of fact, the "natural" supramolecular organization of elastin is in the form of beaded-string-like filaments and not in the form of amyloids whose "in vivo" deposition is associated with some important human diseases. Our work is directed, therefore, to understanding the mechanism by which such hydrophobic sequences form amyloids and any conditions by which they might regress to a non-amyloid filament. The elastin-like sequence here under investigation is the ValGlyGlyValGly pentapeptide that has been previously analyzed both in its monomer and polymer form. In particular, we have focused our investigation on the apparent stability of amyloids formed from poly(ValGlyGlyValGly), and we have observed these fibers evolving to a hydrogel after prolonged aging in water. We will show how atomic force microscopy can be combined with X-ray photoelectron spectroscopy to gain an insight into the spontaneous organization of an elastin-like polypeptide driven by interfacial interactions. The results are discussed also in light of fractal-like assembly and their implications from a biomedical point of view.

Charge transport and intrinsic fluorescence in amyloid-like fibrils

“…Both right-handed ( Fig. 2b) and left-handed helical orientations were found, which is consistent with a recent study (32).…”

Influence of amino acid specificities on the molecular and supramolecular organization of glycine‐rich elastin‐like polypeptides in water

“…These minor contaminants deriving from synthesis and post-synthesis processes [9][10][11][12][13] did not interfere with the spectral elaboration for peak assignment. In fact, the carbon peak distributions follows the stoichiometry of the repeat sequence: C (C,H) :C a :C¼ ¼O 5 7:5:5 where C¼ ¼O is intended as the total carbonyl whether or not involved in H-bonding induced by À ÀNH counterparts (see table and figure).…”

“…[1][2][3][4] These interactions must be controlled to derive information on the aggregation phenomena occurring in important pathologies as amyloidosis, and indeed used, to ensure successful manufacturing of engineered bio-structures. [5][6][7] Such considerations have been of strength in our work on the formation of strong and stiff amyloid-like and non-amyloid fibers or agglomerates from elastin-like polypeptides (ELPs), poly (ValGlyGlyValGly), [8][9][10] and poly(ValGlyGlyLeuGly). [11][12][13] Using AFM to compare the macromolecular structures of these ELPs from aqueous and non-aqueous suspension we have found that the ratio of amyloid-like fibers depends on the water activity in the medium.…”

“…We have ascribed this to the formation of hydrogen-bonded water bridges using XPS with correlation modeling of expected structures. [9][10][11][12][13][14] The self-assembly kinetics have also shown to be modifiable by introduction of suitable amino acids, e.g., leucine in place of valine at the fourth position of the repeat sequence increases the rate of transformation in multiform supramolecular structures. [11][12][13]15 Thus, given the presence within coexisting polymorphs of a stable network of amyloid-like fibers, with poly(ValGlyGlyLeuGly) we have been able to measure the fibers modulus using AFM indentation 16 and this activity will continue to play an important part towards creation of strong biomaterials.…”

“…In previously published work on poly(ValGlyGlyValGly), [8][9][10] AFM was used to reveal the supramolecular structures that are present when droplets of suspended solids are allowed to dry on silicon substrates. In some cases, notably when deposited from CH 3 OH, it was noticed that changes to these structures continued to take place whilst on the substrate.…”