6X9O | pdb_00006x9o

High resolution cryoEM structure of huntingtin in complex with HAP40

• PDB DOI: https://doi.org/10.2210/pdb6X9O/pdb
• EM Map EMD-22106: EMDB EMDataResource

• Classification: PROTEIN BINDING
• Organism(s): Homo sapiens
• Expression System: Spodoptera frugiperda
• Mutation(s): Yes 


• Deposited: 2020-06-03 Released: 2020-06-17 
• Deposition Author(s): Harding, R.J., Deme, J.C., Lea, S.M., Arrowsmith, C.H., Structural Genomics Consortium (SGC)

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Experimental Data Snapshot

• Method: ELECTRON MICROSCOPY
• Resolution: 2.60 Å
• Aggregation State: PARTICLE 
• Reconstruction Method: SINGLE PARTICLE 

Literature

Huntingtin structure is orchestrated by HAP40 and shows a polyglutamine expansion-specific interaction with exon 1.

Harding, R.J., Deme, J.C., Hevler, J.F., Tamara, S., Lemak, A., Cantle, J.P., Szewczyk, M.M., Begeja, N., Goss, S., Zuo, X., Loppnau, P., Seitova, A., Hutchinson, A., Fan, L., Truant, R., Schapira, M., Carroll, J.B., Heck, A.J.R., Lea, S.M., Arrowsmith, C.H.

(2021) Commun Biol 4: 1374-1374

• PubMed: 34880419 
• DOI: https://doi.org/10.1038/s42003-021-02895-4
• Primary Citation Related Structures: 
  6X9O


• PubMed Abstract: 
  

  Huntington's disease results from expansion of a glutamine-coding CAG tract in the huntingtin (HTT) gene, producing an aberrantly functioning form of HTT. Both wildtype and disease-state HTT form a hetero-dimer with HAP40 of unknown functional relevance. We demonstrate in vivo and in cell models that HTT and HAP40 cellular abundance are coupled. Integrating data from a 2.6 Å cryo-electron microscopy structure, cross-linking mass spectrometry, small-angle X-ray scattering, and modeling, we provide a near-atomic-level view of HTT, its molecular interaction surfaces and compacted domain architecture, orchestrated by HAP40. Native mass spectrometry reveals a remarkably stable hetero-dimer, potentially explaining the cellular inter-dependence of HTT and HAP40. The exon 1 region of HTT is dynamic but shows greater conformational variety in the polyglutamine expanded mutant than wildtype exon 1. Our data provide a foundation for future functional and drug discovery studies targeting Huntington's disease and illuminate the structural consequences of HTT polyglutamine expansion.

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Organizational Affiliation: 
• Structural Genomics Consortium, University of Toronto, Toronto, ON, M5G 1L7, Canada. [e-mail].
Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK.
Central Oxford Structural Molecular Imaging Centre, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK.
Center for Structural Biology, Center for Cancer Research, National Cancer Institute, Frederick, MD, 21702, USA.
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute of Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
Netherlands Proteomics Center, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
Princess Margaret Cancer Centre and Department of Medical Biophysics, University of Toronto, Toronto, ON, M5G 1L7, Canada.
Behavioral Neuroscience Program, Department of Psychology, Western Washington University, Bellingham, WA, 98225, USA.
Structural Genomics Consortium, University of Toronto, Toronto, ON, M5G 1L7, Canada.
Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4K1, Canada.
X-ray Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA.
Basic Science Program, Frederick National Laboratory for Cancer Research, SAXS Core of NCI, National Institutes of Health, Frederick, MD, 21701, USA.
Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, M5S 1A8, Canada.
Structural Genomics Consortium, University of Toronto, Toronto, ON, M5G 1L7, Canada. [e-mail].
Princess Margaret Cancer Centre and Department of Medical Biophysics, University of Toronto, Toronto, ON, M5G 1L7, Canada. [e-mail].

Biological Assembly 1  

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Hetero 2-mer - A1B1 

Biological assembly 1 assigned by authors.

Biological Assembly Evidence: light scattering

Macromolecule Content 

• Total Structure Weight: 390.81 kDa 
• Atom Count: 20,899 
• Modeled Residue Count: 2,669 
• Deposited Residue Count: 3,545 
• Unique protein chains: 2

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Huntingtin	A	3,156	Homo sapiens	Mutation(s): 2  Gene Names: HTT, HD, IT15
UniProt & NIH Common Fund Data Resources
Find proteins for P42858 (Homo sapiens) Explore P42858  Go to UniProtKB:  P42858
PHAROS:  P42858 GTEx:  ENSG00000197386

Entity ID: 2
Molecule	Chains	Sequence Length	Organism	Details	Image
40-kDa huntingtin-associated protein	B	389	Homo sapiens	Mutation(s): 0  Gene Names: F8A1, F8A2, F8A3
UniProt & NIH Common Fund Data Resources
Find proteins for P23610 (Homo sapiens) Explore P23610  Go to UniProtKB:  P23610
GTEx:  ENSG00000277150

Experimental Data & Validation

Experimental Data

• Method: ELECTRON MICROSCOPY
• Resolution: 2.60 Å
• Aggregation State: PARTICLE 
• Reconstruction Method: SINGLE PARTICLE 

EM Software:

Task	Software Package	Version
MODEL REFINEMENT	PHENIX
RECONSTRUCTION	RELION	3.1

Structure Validation

Entry History 

Deposition Data

• Released Date: 2020-06-17 
Deposition Author(s): Harding, R.J., Deme, J.C., Lea, S.M., Arrowsmith, C.H., Structural Genomics Consortium (SGC)

Revision History  

• Version 1.0: 2020-06-17
  Type: Initial release
  
• Version 1.1: 2022-03-30
  Changes: Database references
• Version 1.2: 2024-10-23
  Changes: Data collection, Structure summary
• Version 1.3: 2025-05-28
  Changes: Data collection