Self-assembly of beta-sheets into nanostructures by poly(alanine) segments incorporated in multiblock copolymers inspired by spider silk.
Selective replacement of the amorphous peptide domain of a spider silk with poly(ethylene glycol) gave N. clavipes silk-inspired polymers having similar solid-state structures and very good mechanical properties. The tendency of poly(alanine) having appropriate chain length to form beta-sheets and the facility with which the beta-sheets self-assemble have been retained in the polymers. Solid-state (13)C NMR, solid-state FTIR, X-ray diffraction, and AFM studies showed that the polymers formed predominantly antiparallel beta-sheets that self-assembled into discrete nanostructures. The longer the peptide segment was, the greater was the tendency to self-assemble into antiparallel beta-sheet aggregates. AFM revealed that the morphology of the polymers was a microphase-separated architecture that contained irregularly shaped 100-200 nm poly(alanine) nanodomains interspersed within the PEG phase. The results suggest that the poly(alanine) domain influences the solid-state properties of spider silk through beta-sheet self-assembly into temporary cross-links. The results further demonstrate that by selectively replacing certain segments of a naturally occurring biopolymer with a judiciously selected nonnative segment while, at the same time, retaining other segments known to be critical for the essential properties of the native biopolymer, a synthetic polymer with similar properties and function can be obtained.
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Contribution from the Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D002152:Calorimetry, Differential Scanning; D018625:Microscopy, Atomic Force; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013112:Spiders; D014961:X-Ray Diffraction
D010455:Peptides; C019529:polyalanine