Engineering the morphology of a self-assembling protein fibre.

Biological assemblies provide inspiration for the development of new materials for a variety of applications. Our ability to realize this potential, however, is hampered by difficulties in producing and engineering natural biomaterials, and in designing them de novo. We previously described a self-assembling system comprising two short complementary segments of straight synthetic polypeptides (termed standards in this report). Their interaction results in the formation of long fibres--about 50 nm in diameter--that extend straight and without branching for tens to hundreds of micrometres. Our aim is to influence and, ultimately, to control fibre morphology. Here, we show that the standard peptides can be supplemented with special peptides to effect morphological changes in the fibres. Specifically, we created half-sized subunits of the standard peptides, which were combined to make nonlinear peptides. When mixed with the standard peptides, these nonlinear peptides produced kinked, waved and branched fibres. We related the numbers of these features to the special/standard ratios empirically. Furthermore, the extent and frequency of kinking was altered by changing the standard-fibre background: more kinking was observed in a background of thinner, less-stable fibres. The ability to perform such transformations holds promise for bottom-up assembly and engineering responsive biomimetic materials for applications in surface and tissue engineering.