Modulated growth, stability and interactions of liquid-like coacervate assemblies of elastin

Abstract

Elastin self-assembles from monomers into polymer networks that display elasticity and resilience. The first major step in assembly is a liquid-liquid phase separation known as coacervation. This process represents a continuum of stages from initial phase separation to early growth of droplets by coalescence and later "maturation" leading to fiber formation. Assembly of tropoelastin-rich globules is on pathway for fiber formation in vivo. However, little is known about these intermediates beyond their size distribution. Here we investigate the contribution of sequence and structural motifs from full-length tropoelastin and a set of elastin-like polypeptides to the maturation of coacervate assemblies, observing their growth, stability and interaction behavior, and polypeptide alignment within matured globules. We conclude that maturation is driven by surface properties, leading to stabilization of the interface between the hydrophobic interior and aqueous solvent, potentially through structural motifs, and discuss implications for droplet interactions in fiber formation.

Elastin‐Like Peptides (ELPs) – Building Blocks for Stimuli‐Responsive Self‐Assembled Materials

“…Muiznieks et al [8] investigated the growth, stability, and interaction behaviour of colloidal droplets formed in coacervation by comparing the coacervation of full-length native tropoelastin to that of elastin-like polypeptides. All the examined ELPs were the same length as the tropoelastin, but had different sequences.…”

“…They synthesized a polypeptide based on the elastin mimetic sequence [(VPGVG) 14 (VPGKG)] 8 [VPGVG] 40 that forms soluble~10 nm monomers in aqueous solution. Upon heating to 26 8C, large coacervates (~300 nm) were observed ( Figure 3).…”

“…When sufficient hydrophobic amino acids were presented in a periodic sequence, such as (FGG) 8 or (YG) 8 , these highly asymmetric polypeptides self-assembled into cylindrical micelles whose length could be tuned by the sequence of the conjugated part. They found that the (YGG) 8 domain was not sufficiently hydrophobic to drive self-assembly of (VPGAG) 160 ELP, whereas both the (YG) 8 and Y 8 domains drove self-assembly into cylindrical micelles. The R g and R h were determined by light scattering and varied substantially (from 46.1 to 124.4 nm and from 33.0 to 91.4 nm, respectively).…”

“…The hydrophilic domains, rich in lysine and alanine, are involved in the cross-linking of tropoelastin to elastin, while the hydrophobic domains rich in valine, proline, alanine, and glycine, often arranged into repetitive motifs, such as VPG and PGVG, are involved in monomer association in solution, confer elasticity, and contain cell-interacting domains. [3][4][5][6][7][8] Self-assembly is defined as the organization of complexed structures from individual units via specific and/or nonspecific interactions. The inherent amphiphilicity of tropoelastin makes it a natural building block for self-assembled materials.…”

“…These structures then cross-link to form the insoluble elastic fibre. [4,8] The initial phase separation is reversible, and upon cooling, the coacervates dissipate back to soluble monomers. However, if the solution is held above the critical temperature for extended periods, the formation of coacervates is irreversible.…”