Franziska Jehle (1,2), Tobias Priemel (1), Michael Strauss (3), Peter Fratzl (2), Luca Bertinetti (2,4), Matthew Harrington (1,2)
ACS Nano, 15, Issue 4, April 2021: 6829–6838. DOI: 10.1021/acsnano.0c10457

Keywords

self-assembly; mussel byssus; smectic liquid crystal; collagen; block copolymer; FIB-SEM; hierarchical structure

Abstract

Protein-based biological materials are important role models for the design and fabrication of next generation advanced polymers. Marine mussels (Mytilus spp.) fabricate hierarchically structured collagenous fibers known as byssal threads via bottom-up supramolecular assembly of fluid protein precursors. The high degree of structural organization in byssal threads is intimately linked to their exceptional toughness and self-healing capacity. Here, we investigated the hypothesis that multidomain collagen precursor proteins, known as preCols, are stored in secretory vesicles as a colloidal liquid crystal (LC) phase prior to thread self-assembly. Using advanced electron microscopy methods, including scanning TEM and FIB-SEM, we visualized the detailed smectic preCol LC nanostructure in 3D, including various LC defects, confirming this hypothesis and providing quantitative insights into the mesophase structure. In light of these findings, we performed an in-depth comparative analysis of preCol protein sequences from multiple Mytilid species revealing that the smectic organization arises from an evolutionarily conserved ABCBA pentablock copolymer-like primary structure based on demarcations in hydropathy and charge distribution as well as terminal pH-responsive domains that trigger fiber formation. These distilled supramolecular assembly principles provide inspiration and strategies for sustainable assembly of nanostructured polymeric materials for potential applications in engineering and biomedical applications.

How Our Software Was Used

Dragonfly was used for 3D visualization and its movie maker function was used to prepare movies of 3D rendered structures.

Author Affiliation

(1) Dept. of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada.
(2) Max Planck Institute of Colloids and Interfaces, Dept. of Biomaterials, Am Mühlenberg 1, 14476 Potsdam, Germany.
(3) Dept. of Anatomy and Cell Biology, McGill University, 3640 University Street, Montreal, Quebec H3A 0C7, Canada.
(4) BCUBE Center for Molecular Bioengineering, TU Dresden, Tatzberg 41, 01307 Dresden, Germany.