Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 45, Pages 11507-11512Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1810203115
Keywords
biomimetic materials; spider silk formation; hierarchical micelles; natural protein nanostructures
Categories
Funding
- National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health [F32EB021859]
- SDSU
- US Department of Energy [DE-AC52-07NA27344]
- Department of Defense - Air Force Office of Scientific Research (DOD-AFOSR) [FA9550-17-1-0282]
- DOD Defense University Research Instrumentation Program (DURIP) [FA9550-17-1-0409]
- National Science Foundation - Division of Materials Research - Biomaterials (NSF-DMR-BMAT) [1809645]
- Army Research Office (ARO) Multidisciplinary University Research Initiative (MURI) [W911NF-15-1-0568]
- National Institutes of Health
- NATIONAL INSTITUTE OF BIOMEDICAL IMAGING AND BIOENGINEERING [F32EB021859] Funding Source: NIH RePORTER
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Many natural silks produced by spiders and insects are unique materials in their exceptional toughness and tensile strength, while being lightweight and biodegradable-properties that are currently unparalleled in synthetic materials. Myriad approaches have been attempted to prepare artificial silks from recombinant spider silk spidroins but have each failed to achieve the advantageous properties of the natural material. This is because of an incomplete understanding of the in vivo spidroin-to-fiber spinning process and, particularly, because of a lack of knowledge of the true morphological nature of spidroin nanostructures in the precursor dope solution and the mechanisms by which these nanostructures transform into micrometer-scale silk fibers. Herein we determine the physical form of the natural spidroin precursor nanostructures stored within spider glands that seed the formation of their silks and reveal the fundamental structural transformations that occur during the initial stages of extrusion en route to fiber formation. Using a combination of solution phase diffusion NMR and cryogenic transmission electron microscopy (cryo-TEM), we reveal direct evidence that the concentrated spidroin proteins are stored in the silk glands of black widow spiders as complex, hierarchical nanoassemblies (similar to 300 nm diameter) that are composed of micellar subdomains, substructures that themselves are engaged in the initial nanoscale transformations that occur in response to shear. We find that the established micelle theory of silk fiber precursor storage is incomplete and that the first steps toward liquid crystalline organization during silk spinning involve the fibrillization of nanoscale hierarchical micelle subdomains.
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