Microphase Separation Controlled beta-Sheet Crystallization Kinetics in Fibrous Proteins

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Macromolecules

DOI:https://doi.org/10.1021/ma802481p· OSTI ID:980339

Hu, X; Lu, Q; Kaplan, D; Cebe, P

Silk is a naturally occurring fibrous protein with a multiblock chain architecture. As such, it has many similarities with synthetic block copolymers, including the possibility for e-sheet crystallization restricted within the crystallizable blocks. The mechanism of isothermal crystallization kinetics of e-sheet crystals in silk multiblock fibrous proteins is reported in this study. Kinetics theories, such as Avrami analysis which was established for studies of synthetic polymer crystal growth, are for the first time extended to investigate protein self-assembly in e-sheet rich Bombyx mori silk fibroin samples, using time-resolved Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and synchrotron real-time wide-angle X-ray scattering (WAXS). The Avrami exponent, n, was close to 2 for all methods and crystallization temperatures, indicating formation of e-sheet crystals in silk proteins is different from the 3-D spherulitic crystal growth found in synthetic polymers. Observations by scanning electron microscopy support the view that the protein structures vary during the different stages of crystal growth, and show a microphase separation pattern after chymotrypsin enzyme biodegradation. We present a model to explain the crystallization of the multiblock silk fibroin protein, by analogy to block copolymers: crystallization of e-sheets occurs under conditions of geometrical restriction caused by phase separation of the crystallizable and uncrystallizable blocks. This crystallization model could be widely applicable in other proteins with multiblock (i.e., crystallizable and noncrystallizable) domains.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 980339
• Report Number(s): BNL--93257-2010-JA
• Journal Information: Macromolecules, Journal Name: Macromolecules Vol. 42
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ARCHITECTURE
BIODEGRADATION
CALORIMETRY
CHAINS
CHYMOTRYPSIN
COPOLYMERS
CRYSTAL GROWTH
CRYSTALLIZATION
ENZYMES
KINETICS
POLYMERS
PROTEIN STRUCTURE
PROTEINS
SCANNING ELECTRON MICROSCOPY
SCATTERING
SILKWORM
SPECTROSCOPY
SYNCHROTRONS
national synchrotron light source