Light-triggered disassembly of amyloid fibrils

Abstract

There is growing demand for novel methods that could render the controlled disassembly of higher-order structures formed, for example, by peptides. Herein, we demonstrate such a method based on the application of a photocaged variant of the amino acid lysine, namely, lys(Nvoc). Specifically, we introduce lys(Nvoc) into the primary sequence of the amyloidogenic peptide, Aβ(16-22), at a position where the native side chain is known to play a key role in fibril formation via hydrophobic interactions. Both AFM and infrared spectroscopic measurements indicate that the resultant Aβ(16-22) mutant is able to form fibrils whereas, more importantly, the fibrils thus formed can be completely disassembled upon irradiation with near-UV light, which cleaves the photolabile Nvoc moiety and triggers the restoration of the lysine side chain. These results suggest that the generation of a single charge in a highly hydrophobic region of the fibrils is sufficient to promote their dissociation. Thus, we envisage that the current approach will find useful applications wherein controlled structural disassembly or content release is required.

Figure 1

FTIR spectra (in the amide I’ region) of a 1.1 mM mixture of F19K* (95%) and Aβ_16-22 (5%) in D₂O (pH 2) acquired at different delay times relative to sample preparation, as indicated. The arrows depict the growth of two characteristic spectral features of tightly packed antiparallel β-sheets.

Figure 2

A representative AFM image of the F19K* solution after 10 days of incubation, showing the formation of typical amyloid fibrils.

Figure 3

FTIR spectra (in the amide I’ region) of the F19K* aggregate solution in Figure 1, acquired at various times after irradiation with 355 nm light. The arrows depict the direction of increasing irradiation times. Also shown in the inset is the absorbance at 1620 cm⁻¹ as a function of the irradiation time. The line is the fit of these data to a single-exponential function with a time constant of ~1 h.

Figure 4

A representative AFM image of the F19K* solution after 7 hours of irradiation.

Figure 5

Representative AFM images of a ~500 μM peptide solution containing wild-type Aβ_16-22 and F19K*, at a molar ratio of about 1:1.5, (A) before and (B) after ~7 hours of irradiation.

Figure 6

FTIR spectra (in the amide I’ region) of a 250 μM solution (pH 2) of a 3:1 mixture of K16K* and wild-type Aβ_16-22 with irradiation at 355 nm for the indicated amount of time. The comparatively lower concentration of the K16K* used herein was due to its poor solubility and higher aggregation propensity.

Scheme 1

Irradiation of lys(Nvoc) (A) with near-UV light results in photocleavage of the Nvoc cage, generating a charged lysine residue (B) and the cage photoproduct (C).