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Published on: May 18, 2017
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Intermediate filament structure in fully differentiated (oxidised) trichocyte keratin
R D Bruce Fraser1, David A D Parry2
1Institute of Fundamental Sciences, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand.
Journal of Structural Biology
|September 12, 2017
Summary
New X-ray analysis supports the (8+0) protofilament model for keratin intermediate filaments (IFs), resolving a 50-year debate. The (7+1) model is inconsistent with structural data and presents steric hindrance issues.
Area of Science:
- Biochemistry
- Structural Biology
- Materials Science
Background:
- Debate exists regarding the substructure of differentiated trichocyte keratin intermediate filaments (IFs).
- Transmission electron microscopy (TEM) observations in transverse section have shown varied appearances, interpreted as "ring" ((8+0) protofilament arrangement) or "ring-core" ((7+1) protofilament arrangement).
Purpose of the Study:
- To resolve the debate on the substructure of trichocyte keratin intermediate filaments.
- To determine whether the (8+0) or (7+1) protofilament arrangement best fits experimental data.
Main Methods:
- Analysis of the fine structure of the 1nm equatorial region of the X-ray diffraction pattern of quill.
- Comparison of observed X-ray diffraction patterns with predicted patterns for (8+0) and (7+1) models.
Main Results:
- The observed X-ray diffraction pattern is consistent with the (8+0) protofilament model.
- The observed X-ray diffraction pattern is inconsistent with the (7+1) protofilament model.
- Steric hindrance issues were identified within the (7+1) model.
Conclusions:
- The (8+0) protofilament arrangement is the correct model for trichocyte keratin intermediate filaments.
- The "ring-core" appearance in TEM is explained by the positioning of molecular domains, not a central protofilament.
- The H1 subdomain likely plays a crucial role in the assembly of trichocyte keratin IFs.
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