Hagfish Slime Threads - The Functional Fold: Amyloid Structures in Nature - page 20

What kind of function could such an unusual material (or event)
fulfil for the hagfish? One hypothesis is that the slime acts as a
deterrent to gill breathing predators. Our data are consistent with this
idea—the slime does not appear adapted to binding sea water, but
rather to slowing it down to a trickle, which would have devastating
effects on the function of fish gills.

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Indeed, it has been shown more
directly that hagfish slime is capable of dramatically increasing
the resistance of gills in experiments with isolated fish heads

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(Fig. 2.3).

2.2 Are Hagfish Slime Threads “Disposable
Amyloid”?

One of the keys to the unique properties of hagfish slime is the rapid
deployment of the slime threads from a tight, coiled state to one in
which they are unravelled and extended. The presence of the threads
imparts long-range order to the slime and allows it to remain as a
semi-coherent mass even at the extremely low concentrations of
protein and glycoprotein in mature slime (approximately 40 mg
dry weight/l). In their native state, the slime threads are 1-3 μm in
diameter and more than 10 cm long,

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but they have the ability to
stretch to more than three times this length when they are loaded in
tension. It is under these conditions that their constituent proteins

take on an amyloid-like structure.
The amyloid-like nature of hagfish slime threads was first
detected by staining the threads with Congo red, thus revealing
amyloid-like metachromasia and birefringence.

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Further invest-
igations showed that only stretched slime threads exhibit these
properties, while unstretched, native threads do not. These
experiments led to further exploration of what kind of deformations
of the slime are required to bring about the transformation of slime
thread proteins into an amyloid-like state. The answer is that hagfish
slime, as produced in a still aquarium, results in little Congo red
metachromasia by slime threads, as long as the slime is handled
gently when it is isolated and stained. If the slime is subjected to a
mild mechanical stimulus, as might occur when a hagfish or other
animal thrashes within it, most of the threads are transformed into a
state in which they exhibit Congo red metachromasia (Fig. 2.4).

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