9RKP | pdb_00009rkp

Crystal structure of the coiled-coil based fibril core of the tardigrade CAHS-8 protein

• PDB DOI: https://doi.org/10.2210/pdb9RKP/pdb

• Classification: PROTEIN FIBRIL
• Organism(s): Hypsibius exemplaris
• Expression System: Escherichia coli BL21(DE3)
• Mutation(s): Yes 


• Deposited: 2025-06-13 Released: 2026-01-14 
• Deposition Author(s): Malki, A., Nanao, M.H., Blackledge, M.
• Funding Organization(s): French Alternative Energies and Atomic Energy Commission (CEA)

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free: 
  0.289 (Depositor), 0.289 (DCC) 
• R-Value Work: 
  0.250 (Depositor), 0.250 (DCC) 
• R-Value Observed: 
  0.252 (Depositor) 

Starting Model: in silico

Literature

Fibril Structure of Desiccation-Protective Tardigrade Protein CAHS-8.

Malki, A., Teulon, J.M., Mikkola, E.A., Maurin, D., Pellequer, J.L., Nanao, M.H., Blackledge, M.

(2026) Angew Chem Int Ed Engl 65: e19912-e19912

• PubMed: 41474256 
• DOI: https://doi.org/10.1002/anie.202519912
• Primary Citation Related Structures: 
  9RKP


• PubMed Abstract: 
  

  Cytosolic Abundant Heat-Soluble (CAHS) proteins are thought to be responsible for protection of tardigrades against conditions of extreme environmental stress, in particular desiccation. Hypsibius exemplaris CAHS-8 is intrinsically disordered in solution, undergoing conformational transformation as a function of stress, assembling into fibres that form a hydrogel. Here we present the crystal structure of the fibrils of CAHS-8, comprising a single 101 residue-long helix, forming an atypical 90 amino-acid coiled-coil dimer exhibiting non-canonical periodicities and assembling into fibrils via a second coiled coil interface associating adjacent dimers via the opposing face of the helix. Combination with electron microscopy, atomic force microscopy and disorder modelling provides structural insight into the details of this assembly that is essential for cell survival. Individual fibrils appear to interact in a pairwise manner, possibly via their intrinsically disordered tails, forming straight fibres.

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Organizational Affiliation: 
• Univ. Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale, Grenoble, France.
Research & Early Development, Discovery Sciences, Roche Diagnostics GmbH, 82377, Penzberg, Germany.
Structural Biology Group, European Synchrotron Radiation Facility, Grenoble, F-38000, France.

Biological Assembly 1  

Global Symmetry: Cyclic - C2  (Explore in 3D)
Global Stoichiometry: Homo 2-mer - A2 

Biological assembly 1 assigned by authors.

Biological Assembly Evidence: NMR relaxation study, homology

Biological Assembly 2  

Global Symmetry: Cyclic - C2  (Explore in 3D)
Global Stoichiometry: Homo 2-mer - A2 

Biological assembly 2 assigned by authors.

Biological Assembly Evidence: NMR relaxation study, homology, cross-linking

Biological Assembly 3  

Global Symmetry: Cyclic - C2  (Explore in 3D)
Global Stoichiometry: Homo 12-mer - A12 

Biological assembly 3 assigned by authors.

Biological Assembly Evidence: NMR relaxation study, microscopy, electron microscopy, cross-linking

Macromolecule Content 

• Total Structure Weight: 26.33 kDa 
• Atom Count: 1,799 
• Modeled Residue Count: 211 
• Deposited Residue Count: 220 
• Unique protein chains: 1

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Cytosolic-abundant heat soluble protein 94063	A, B	110	Hypsibius exemplaris	Mutation(s): 2  Gene Names: CAHS 94063, CAHS-8
UniProt
Find proteins for P0CU50 (Hypsibius exemplaris) Explore P0CU50  Go to UniProtKB:  P0CU50

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free:  0.289 (Depositor), 0.289 (DCC) 
• R-Value Work:  0.250 (Depositor), 0.250 (DCC) 
• R-Value Observed: 0.252 (Depositor) 

Space Group: C 1 2 1

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 61.83	α = 90
b = 55.45	β = 103.85
c = 96.38	γ = 90

Software Package:

Software Name	Purpose
PHENIX	refinement
XDS	data reduction
XSCALE	data scaling
Arcimboldo	phasing

Structure Validation

Entry History 

& Funding Information

Deposition Data

• Released Date: 2026-01-14 
Deposition Author(s): Malki, A., Nanao, M.H., Blackledge, M.

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Funding Organization	Location	Grant Number
French Alternative Energies and Atomic Energy Commission (CEA)	France	--

Revision History  

• Version 1.0: 2026-01-14
  Type: Initial release
  
• Version 1.1: 2026-02-18
  Changes: Database references
• Version 1.2: 2026-02-25
  Changes: Database references