Self-assembling peptides
are being applied both in the biomedical
area and as building blocks in nanotechnology. Their applications
are closely linked to their modes of self-assembly, which determine
the functional nanostructures that they form. This work brings together
two structural elements that direct nanoscale self-association in
divergent directions: proline as a β-breaker and the β-structure-associated
diphenylalanine motif, into a single tripeptide sequence. Amino acid
chirality was found to resolve the tension inherent to these conflicting
self-assembly instructions. Stereoconfiguration determined the ability
of each of the eight possible Pro-Phe-Phe stereoisomers to self-associate
into diverse nanostructures, including nanoparticles, nanotapes, or
fibrils, which yielded hydrogels with gel-to-sol transition at a physiologically
relevant temperature. Three single-crystal structures and all-atom
molecular dynamics simulations elucidated the ability of each peptide
to establish key interactions to form long-range assemblies (
i,e.
, stacks leading to gelling fibrils), medium-range assemblies
(
i.e.
, stacks yielding nanotapes), or short-range
assemblies (
i.e.
, dimers or trimers that further
associated into nanoparticles). Importantly, diphenylalanine is known
to serve as a binding site for pathological amyloids, potentially
allowing these heterochiral systems to influence the fibrillization
of other biologically relevant peptides. To probe this hypothesis,
all eight Pro-Phe-Phe stereoisomers were tested
in vitro
on the Alzheimer’s disease-associated Aβ(1–42)
peptide. Indeed, one nonfibril-forming stereoisomer effectively inhibited
Aβ fibrillization through multivalent binding between diphenylalanine
motifs. This work thus defined heterochirality as a useful feature
to strategically develop future therapeutics to interfere with pathological
processes, with the additional value of resistance to protease-mediated
degradation and biocompatibility.