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Human keratin 1/10‐1B tetramer structures reveal a knob‐pocket mechanism in intermediate filament assembly
Author(s) -
Eldirany Sherif A,
Ho Minh,
Hinbest Alexander J,
Lomakin Ivan B,
Bunick Christopher G
Publication year - 2019
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.15252/embj.2018100741
Subject(s) - biology , tetramer , protein filament , mechanism (biology) , intermediate filament , keratin , microbiology and biotechnology , biophysics , genetics , cytoskeleton , biochemistry , enzyme , cell , physics , quantum mechanics
To characterize keratin intermediate filament assembly mechanisms at atomic resolution, we determined the crystal structure of wild‐type human keratin‐1/keratin‐10 helix 1B heterotetramer at 3.0 Å resolution. It revealed biochemical determinants for the A 11 mode of axial alignment in keratin filaments. Four regions on a hydrophobic face of the K1/K10‐1B heterodimer dictated tetramer assembly: the N‐terminal hydrophobic pocket (defined by L227 K1 , Y230 K1 , F231 K1 , and F234 K1 ), the K10 hydrophobic stripe, K1 interaction residues, and the C‐terminal anchoring knob (formed by F314 K1 and L318 K1 ). Mutation of both knob residues to alanine disrupted keratin 1B tetramer and full‐length filament assembly. Individual knob residue mutant F314A K1 , but not L318A K1 , abolished 1B tetramer formation. The K1‐1B knob/pocket mechanism is conserved across keratins and many non‐keratin intermediate filaments. To demonstrate how pathogenic mutations cause skin disease by altering filament assembly, we additionally determined the 2.39 Å structure of K1/10‐1B containing a S233L K1 mutation linked to epidermolytic palmoplantar keratoderma. Light scattering and circular dichroism measurements demonstrated enhanced aggregation of K1 S233L /K10‐1B in solution without affecting secondary structure. The K1 S233L /K10‐1B octamer structure revealed S233L K1 causes aberrant hydrophobic interactions between 1B tetramers.