6 research outputs found
Rapid Filament Supramolecular Chirality Reversal of HETâs (218â289) Prion Fibrils Driven by pH Elevation
Amyloid
fibril polymorphism is not well understood despite its
potential importance for biological activity and associated toxicity.
Controlling the polymorphism of mature fibrils including their morphology
and supramolecular chirality by postfibrillation changes in the local
environment is the subject of this study. Specifically, the effect
of pH on the stability and dynamics of HET-s (218â289) prion
fibrils has been determined through the use of vibrational circular
dichroism (VCD), deep UV resonance Raman, and fluorescence spectroscopies.
It was found that a change in solution pH causes deprotonation of
Asp and Glu amino acid residues on the surface of HET-s (218â289)
prion fibrils and triggers rapid transformation of one supramolecular
chiral polymorph into another. This process involves changes in higher
order arrangements like lateral filament and fibril association and
their supramolecular chirality, while the fibril cross-β core
remains intact. This work suggests a hypothetical mechanism for HET-s
(218â289) prion fibril refolding and proposes that the interconversion
between fibril polymorphs driven by the solution environment change
is a general property of amyloid fibrils
Rapid Filament Supramolecular Chirality Reversal of HETâs (218â289) Prion Fibrils Driven by pH Elevation
Amyloid
fibril polymorphism is not well understood despite its
potential importance for biological activity and associated toxicity.
Controlling the polymorphism of mature fibrils including their morphology
and supramolecular chirality by postfibrillation changes in the local
environment is the subject of this study. Specifically, the effect
of pH on the stability and dynamics of HET-s (218â289) prion
fibrils has been determined through the use of vibrational circular
dichroism (VCD), deep UV resonance Raman, and fluorescence spectroscopies.
It was found that a change in solution pH causes deprotonation of
Asp and Glu amino acid residues on the surface of HET-s (218â289)
prion fibrils and triggers rapid transformation of one supramolecular
chiral polymorph into another. This process involves changes in higher
order arrangements like lateral filament and fibril association and
their supramolecular chirality, while the fibril cross-β core
remains intact. This work suggests a hypothetical mechanism for HET-s
(218â289) prion fibril refolding and proposes that the interconversion
between fibril polymorphs driven by the solution environment change
is a general property of amyloid fibrils
Structural and Mechanical Properties of Amyloid Beta Fibrils: A Combined Experimental and Theoretical Approach
In this combined
experimental (deep ultraviolet resonance Raman
(DUVRR) spectroscopy and atomic force microscopy (AFM)) and theoretical
(molecular dynamics (MD) simulations and stressâstrain (SS))
study, the structural and mechanical properties of amyloid beta (Aβ40)
fibrils have been investigated. The DUVRR spectroscopy and AFM experiments
confirmed the formation of linear, unbranched and β-sheet rich
fibrils. The fibrils (Aβ40)<sub><i>n</i></sub>, formed
using <i>n</i> monomers, were equilibrated using all-atom
MD simulations. The structural properties such as β-sheet character,
twist, interstrand distance, and periodicity of these fibrils were
found to be in agreement with experimental measurements. Furthermore,
Youngâs modulus (<i>Y</i>) = 4.2 GPa computed using
SS calculations was supported by measured values of 1.79 Âą 0.41
and 3.2 Âą 0.8 GPa provided by two separate AFM experiments. These
results revealed size dependence of structural and material properties
of amyloid fibrils and show the utility of such combined experimental
and theoretical studies in the design of precisely engineered biomaterials
Is Supramolecular Filament Chirality the Underlying Cause of Major Morphology Differences in Amyloid Fibrils?
The unique enhanced
sensitivity of vibrational circular dichroism
(VCD) to the formation and development of amyloid fibrils in solution
is extended to four additional fibril-forming proteins or peptides
where it is shown that the sign of the fibril VCD pattern correlates
with the sense of supramolecular filament chirality and, without exception,
to the dominant fibril morphology as observed in AFM or SEM images.
Previously for insulin, it has been demonstrated that the sign of
the VCD band pattern from filament chirality can be controlled by
adjusting the pH of the incubating solution, above pH 2 for ânormalâ
left-hand-helical filaments and below pH 2 for âreversedâ
right-hand-helical filaments. From AFM or SEM images, left-helical
filaments form multifilament braids of left-twisted fibrils while
the right-helical filaments form parallel filament rows of fibrils
with a flat tape-like morphology, the two major classes of fibril
morphology that from deep UV resonance Raman scattering exhibit the
same cross-β-core secondary structure. Here we investigate whether
fibril supramolecular chirality is the underlying cause of the major
morphology differences in all amyloid fibrils by showing that the
morphology (twisted versus flat) of fibrils of lysozyme, apo-Îą-lactalbumin,
HET-s (218â289) prion, and a short polypeptide fragment of
transthyretin, TTR (105â115), directly correlates to their
supramolecular chirality as revealed by VCD. The result is strong
evidence that the chiral supramolecular organization of filaments
is the principal underlying cause of the morphological heterogeneity
of amyloid fibrils. Because fibril morphology is linked to cell toxicity,
the chirality of amyloid aggregates should be explored in the widely
used <i>in vitro</i> models of amyloid-associated diseases
Purple Fibrils: A New Type of Protein Chromophore
A purple
color is formed during the fibrillation of lysozyme, a
well-studied protein lacking a prosthetic group. The application of
Raman spectroscopy, electron paramagnetic resonance and UVâvis
absorption spectroscopy indicates the formation of a sulfurâ´Ď-bonded
radical cation due to the methionine-phenylalanine interaction, which
is consistent with a small molecule model reported in the literature.
A purple chromophore with characteristic 550 nm absorption is formed
due to a specific orientation of the sulfur-centered radical cation
and a phenyl ring stabilized by the fibril framework. A specific fibril
conformation and the resulting formation of the chromophore are controlled
reversibly by varying the pH. This is the first known example of a
side chain self-assembled chromophore formed due to protein aggregation