Phase transitions
have an essential role in the assembly of nature’s
protein-based materials into hierarchically organized structures,
yet many of the underlying mechanisms and interactions remain to be
resolved. A central question for designing proteins for materials
is how the protein architecture and sequence affects the nature of
the phase transitions and resulting assembly. In this work, we produced
82 kDa (1×), 143 kDa (2×), and 204 kDa (3×) silk-mimicking
proteins by taking advantage of protein ligation by SpyCatcher/Tag
protein-peptide pair. We show that the three silk proteins all undergo
a phase transition from homogeneous solution to assembly formation.
In the assembly phase, a length- and concentration-dependent transition
between two distinct assembly morphologies, one forming aggregates
and another coacervates, exists. The coacervates showed properties
that were dependent on the protein size. Computational modeling of
the proteins by a bead-spring model supports the experimental results
and provides us a possible mechanistic origin for the assembly transitions
based on architectures and interactions.
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