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Printable Handouts
Navigable Slide Index
- Introduction
- Talk outline
- Defining features of amyloid fibrils
- The amyloid fibril structure in pathology and biology
- Disease-associated amyloid fibrils vs. functional amyloid fibrils
- Fibrillar rodlets form amphipathic layers on aerial fungal structures
- Fungal hydrophobin rodlets have amyloid characteristics
- Why do fungi need hydrophobins?
- Class I and class II hydrophobin sequences
- Rodlet formation is limited to a hydrophobic:hydrophilic interface
- EAS hydrophobin monomer and rodlet layers are amphipathic
- Hydrophobin self-assembly into amyloid-structured rodlets
- The hydrophobin RodA from Aspergillus fumigatus
- Two loops are both involved in RodA functional amyloid assembly
- In vitro rodlet assembly kinetics reflected on A. fumigatus spores
- Hydrophobin functional amyloid:“ protein cling wrap”
- Necroptosis signaling pathways and amyloid complexes
- RHIM-containing region of M45 from murine cytomegalovirus protects against necroptosis
- The RHIM of viral M45 is amyloidogenic, like RIPK1 and RIPK3
- Viral M45 is not a simple inhibitor of RIPK3 amyloid formation
- M45 forms heteromeric fibrils with RIPK3: the tetrad is critical
- M45:RIPK3 assembly is favoured over RIPK1:RIPK3 assembly
- Viral M45 RHIM substitutes for cellular RHIM in decoy amyloids
- Other viruses express amyloid-forming RHIM proteins to inhibit host cell death
- The virus:host arms race
Topics Covered
- Functional amyloid fibrils
- Defining features of amyloid fibrils
- Amyloid fibril structure
- Disease-associated amyloid fibrils
- Fibrillar rodlets
- Fungal hydrophobin
- Aspergillus fumigatus
- RodA
- Necroptosis
- RHIM motif
Links
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Therapeutic Areas:
Talk Citation
Sunde, M. (2024, April 30). Functional amyloid fibrils from fungi and viruses [Video file]. In The Biomedical & Life Sciences Collection, Henry Stewart Talks. Retrieved August 23, 2024, from https://doi.org/10.69645/KQLG7712.Export Citation (RIS)
Publication History
Financial Disclosures
- No financial or commercial matters to disclose.
A selection of talks on Biochemistry
Transcript
Please wait while the transcript is being prepared...
0:00
This talk focuses on
Functional Amyloid Fibrils
from Fungi and Viruses.
The structures of
these fibrils and how
the unique amyloid structure
gives rise to
biological functions.
I'm Margaret Sunde,
a Professor in Molecular
Biomedicine from
the University of
Sydney in Australia.
0:22
The talk is in three main parts.
Firstly, I will discuss
what amyloid fibrils are,
and the similarities
and differences between
amyloid fibrils associated
with diseases or pathology
and those amyloid
fibrils which have
distinct biological
roles or activities.
In the second part,
I'll focus on
one type of functional amyloid
produced by filamentous fungi.
These are fibrils composed of
fungal proteins known
as hydrophobins.
I will explain what we know
about their structure,
how these fibrils
form, and provide
an example of how they
impact human health.
In the final section,
I will explain the role that
functional amyloid fibrils play
in mammalian cell
death pathways.
I will show you how certain
viral proteins that can form
amyloid fibrils are
able to inhibit
the host's innate response
to viral infection.
1:15
What do we mean by
amyloid fibrils?
Insoluble fibrillar protein
deposits were first
described in association with
human disease in the 1800s.
Since the early 2000s,
protein fibrils with
similar structures
have been identified in
organisms across the tree
of life including bacteria,
viruses, fungi,
plants, and mammals.
Where these fibrils are
not associated with
any disease but they do
have biological functions.
In both disease-associated
and natural or
functional fibrils,
the precursor proteins which
polymerize to form
the fibrils have
a wide range of sizes,
structures, and sequences.
However, when these
diverse proteins
polymerize to form
protein amyloid fibrils,
the fibrils all exhibit
common structural,
tinctorial: that is how they
stain, and
morphological features.
These can be considered
the defining characteristics of
amyloid and I'll
illustrate these here.
To start with, they are
all generally long,
straight, and unbranching,
and approximately
ten nanometers wide.
You can see them in this
electron micrograph here.
A good example of
amyloid fibrils.
All amyloid fibrils
also stain in
a characteristic way with the
dyes Congo red and Thioflavin T.
Here I've illustrated
an amyloid deposit
stained with Congo red.
In the bright field
image on the left,
you can see the uptake
of the red dye.
However, when this is viewed
between cross-polarizers,
the amyloid deposits appear
with green birefringence due to
the preferential ordering of
the di-molecules along
the long amyloid fibrils.
Finally, all amyloid
fibrils exhibit
a similar cross-β X-ray
fiber diffraction pattern,
indicating that they all have
a similar underlying
molecular scaffold.
The X-ray fiber
diffraction pattern
is illustrated on
the bottom right.
It consists of two
major reflections,
a strong 4.8 angstrom
meridional reflection
that comes from
a regular spacing along
the fibril's long axis.
In the cartoon, you can see that
this 4.8 Angstrom spacing
comes from the distance between
β-strands in the direction
of intrastrand hydrogen bonding.
A weaker and more diffuse
equatorial spacing
lies at right angles to this,
and is 8 to 12 angstroms.
This comes from a more
variable inter-sheet distance.
Together these make
up a β-sheet rich,
poor architecture that is
shared by all amyloid fibrils.