Strategies and Molecular Design Criteria for 3D Printable Hydrogels

The vertebrate collagen superfamily now includes over 50 collagens and collagen-like proteins Here, their different structures are described, as well as their diverse forms of supramolecular assembly Also presented here are the various steps in collagen biosynthesis, both intracellular and extracellular, and the functions of the collagen-specific post-translational modifications Assembly of collagen fibrils, both in vitro and in vivo, is reviewed, including the mechanisms that control this process and the interactions involved Finally, recent developments in the supramolecular assembly of collagen-like peptides are discussed

Collagen Diversity, Synthesis and Assembly

Des courbes d'extinction observees dans des spherulites de plusieurs polymeres paraissent etre en bon accord avec les courbes d'extinction theoriques calculees dans la 1 ere partie. Les resultats indiquent l'existence d'une rotation reguliere de l'orientation du cristal dans beaucoup de ces spherulites. Dans le cas du polyethylene la morphologie des spherulites est expliquee en detail. On considere les mecanismes suivant lesquels les spherulites fibreux sont formes dans des polymeres fondus. On montre que les fibrilles radiaires croissent et se ramifient comme des fins cristaux dendritiques. Sur cette base on explique qualitativement les orientations moleculaires preferentielles dans des spherulites polymeriques.

The Optical Behavior of Spherulites in Crystalline Polymers. Part II. The Growth and Structure of the Spherulites

This review discusses liquid crystal phase formation by biopolymers in solution. Lyotropic mesophases have been observed for several classes of biopolymer including DNA, peptides, polymer/peptide conjugates, glycopolymers and proteoglycans. Nematic or chiral nematic (cholesteric) phases are the most commonly observed mesophases, in which the rod-like fibrils have only orientational order. Hexagonal columnar phases are observed for several systems (DNA, PBLG, polymer/peptide hybrids) at higher concentration. Lamellar (smectic) phases are reported less often, although there are examples such as the layer arrangement of amylopectin side chains in starch. Possible explanations for the observed structures are discussed. The biological role of liquid crystal phases for several of these systems is outlined. Commonly, they may serve as a template to align fibrils for defined structural roles when the biopolymer is extruded and dried, for instance in the production of silk by spiders or silkworms, or of chitin in arthropod shells. In other cases, liquid crystal phase formation may occur in vivo simply as a consequence of high concentration, for instance the high packing density of DNA within cell nuclei.

Liquid crystal phase formation by biopolymers

Self-association of collagen triple helic peptides into higher order structures.

The relationship between primary sequence and collagen triple-helix formation is relatively well characterized, while higher levels of structural assembly from these sequences is poorly understood. To address this gap, a new collagen-like triblock peptide design was used to study the relationship between amino acid sequence and supramolecular assembly. Four collagen-like peptides with the sequence (Glu)5(Gly–Xaa–Hyp–Gly–Pro–Hyp)6(Glu)5 and corresponding to Xaa = alanine, proline, serine, or valine, and an analogous peptide without the glutamic acid end blocks, were solubilized in water at high concentrations (20–150 mg/mL) and analyzed in optical polarizing microscopy and transmission electron microscopy. Some of the peptides self-assembled into supramolecular structures, the nature of which was determined by the core collagen-like sequence. The globular end blocks appeared necessary for these short triple-helix-forming peptides to spontaneously organize into supramolecular structures in solution and also provided enhanced thermal stability based on CD analysis. The results indicate a strong dependence of the peptide triblock assembly behavior on the identity of the guest residue Xaa; nematic order when Xaa was valine, no organization when Xaa was serine, and banded spherulites displaying a cholesteric-like twist when Xaa was proline or alanine. According to these results, the identity of the amino acid in position Xaa of the triplet Gly–Xaa–Yaa dramatically determined the type of supramolecular assembly formed by short triple helices based on collagen-triblock like sequences. Moreover, the structural organization observed for these collagen-triblock peptides was analogous to some assemblies observed for native collagen in vivo and in vitro. The amino acid sequence in the native collagen proteins may therefore be a direct determinant of the different supramolecular architectures found in connective tissues. © 2003 Wiley Periodicals, Inc. Biopolymers 70:435–444, 2003

Lars Waldmann

Papers

Supramolecular assembly of collagen triblock peptides.