Hagfish Slime Threads - The Functional Fold: Amyloid Structures in Nature - page 27

this kind of behaviour has been observed, and we currently do not
have a firm grasp of its molecular underpinnings.
Further clues about the nature of the stretch-induced conformat-
ional transitions that occur in slime threads have come from wide
angle synchrotron X-ray diffraction (Fig. 2.8).

a b c

Figure 2.8 X-ray diffraction of hagfish threads strained in sea water. 11

(a) Unstrained threads exhibit a typical pattern, whereas

threads stretched to a strain of 1.0 exhibit a typical

α

β

pattern
(c). Threads strained to 0.60 exhibit a mixed pattern (b).
Diffraction maxima are labelled according to the molecular
spacings (in angstroms) to which they correspond. With
permission from . 11 Biophysical Journal

Native slime threads exhibit a pattern that is typical for
α

-keratins such as wool, with a meridional reflection at 5.15 Å, and
an equatorial reflection at 9.8 Å.

11

These peaks correspond to the
axial rise of coiled coils, and the spacing between adjacent coiled
coils, respectively.

22,23

Threads stretched to a strain of 100% exhibit

β

a typical “ -pattern”, with strong equatorial reflections at 4.7 Å and

9.7 Å, and a meridional refection at 3.3 Å. These peaks correspond

to the spacings between protein chains within

11

β

-sheets, the spacings

β β

between adjacent -sheets within -sheet crystals, and the axial rise

23,24

of Bundles of threads stretched to a strain

of 60% exhibit a mixed diffraction pattern, with all of the above
reflections present. Together with the Congo red results, these data
suggest that that the post-yield plastic deformation of slime threads
corresponds to a stress-induced conversion of coiled coil

β

-sheets, respectively.

α

-helices

11

into

These results point to some interesting differences between the
structure of “conventional” amyloid fibrils and slime threads. One
of the hallmarks of conventional amyloid is a cross-

β

-sheets that in turn stack into

β

-sheets crystals.

β

structure, in

β

which polypeptides are arranged into -sheets that are oriented