Chemistry Reference
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structures were formed when charged histidine prevented the formation of helical
structures.
Wagner and coworkers (2005) addressed the issue of fiber maturation in their
designed self-assembled nanoropes and nanofilaments. The peptide (CpA) contains
two identical GCN4 subunits (each having a two-heptad unit) that are linked by a
dipeptide subunit (Ala-Ala). The insertion of Ala-Ala changes the inherent pattern
of hydrophobic amino acids on GCN4 that are generally aligned on the same
phase in the interior of the coiled coils. The model (Fig. 14.4) instead showed a
phase shift of heptad repeats, producing two hydrophobic clusters oriented at 2008
with respect to one another. Thus, the self-assembled staggered coiled coil dimer
was facilitated and specified by hydrophobic interaction that favors fiber axial
growth rather than lateral aggregation.
Because the self-assembly takes place between a pair of two-heptad peptides
through hydrophobic interaction, a relatively high concentration of salt needs to be
added to enhance the hydrophobic effects. In addition, at the N-terminus, Cys was
introduced to promote the association of the dimer and further polymerization.
Figure 14.4 Primary sequence and molecular model of a coiled coil dimer and self-
assembled polymer. The final bundle fiber structure is shown at the bottom. Reprinted from
Wagner et al. (2005). Copyright 2005 National Academy of Sciences.
