Controlling the Oligomerization State of Aβ-Derived Peptides with Light

A key
challenge in studying the biological and biophysical properties
of amyloid-forming peptides is that they assemble to form heterogeneous
mixtures of soluble oligomers and insoluble fibrils. Photolabile protecting
groups have emerged as tools to control the properties of biomolecules
with light. Blocking intermolecular hydrogen bonds that stabilize
amyloid oligomers provides a general strategy to control the biological
and biophysical properties of amyloid-forming peptides. In this paper
we describe the design, synthesis, and characterization of macrocyclic
β-hairpin peptides that are derived from amyloidogenic peptides
and contain the N-2-nitrobenzyl photolabile protecting
group. Each peptide contains two heptapeptide segments from Aβ16–36 or Aβ17–36 constrained
into β-hairpins. The N-2-nitrobenzyl group
is appended to the amide backbone of Gly33 to disrupt the
oligomerization of the peptides by disrupting intermolecular hydrogen
bonds. X-ray crystallography reveals that N-2-nitrobenzyl
groups can either block assembly into discrete oligomers or permit
formation of trimers, hexamers, and dodecamers. Photolysis of the N-2-nitrobenzyl groups with long-wave UV light unmasks the
amide backbone and alters the assembly and the biological properties
of the macrocyclic β-hairpin peptides. SDS–PAGE studies
show that removing the N-2-nitrobenzyl groups alters
the assembly of the peptides. MTT conversion and LDH release assays
show that decaging the peptides induces cytotoxicity. Circular dichroism
studies and dye leakage assays with liposomes reveal that decaging
modulates interactions of the peptides with lipid bilayers. Collectively,
these studies demonstrate that incorporating N-2-nitrobenzyl
groups into macrocyclic β-hairpin peptides provides a new strategy
to probe the structures and the biological properties of amyloid oligomers.