Abstract

Huntingtin (HTT) is a large (348 kDa) protein that is essential for embryonic development and is involved in diverse cellular activities such as vesicular transport, endocytosis, autophagy and the regulation of transcription1,2. Although an integrative understanding of the biological functions of HTT is lacking, the large number of identified HTT interactors suggests that it serves as a protein–protein interaction hub1,3,4. Furthermore, Huntington’s disease is caused by a mutation in the HTT gene, resulting in a pathogenic expansion of a polyglutamine repeat at the amino terminus of HTT5,6. However, only limited structural information regarding HTT is currently available. Here we use cryo-electron microscopy to determine the structure of full-length human HTT in a complex with HTT-associated protein 40 (HAP40; encoded by three F8A genes in humans)7 to an overall resolution of 4 Å. HTT is largely α-helical and consists of three major domains. The amino- and carboxy-terminal domains contain multiple HEAT (huntingtin, elongation factor 3, protein phosphatase 2A and lipid kinase TOR) repeats arranged in a solenoid fashion. These domains are connected by a smaller bridge domain containing different types of tandem repeats. HAP40 is also largely α-helical and has a tetratricopeptide repeat-like organization. HAP40 binds in a cleft and contacts the three HTT domains by hydrophobic and electrostatic interactions, thereby stabilizing the conformation of HTT. These data rationalize previous biochemical results and pave the way for improved understanding of the diverse cellular functions of HTT.

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Acknowledgements

We thank J. Plitzko for electron microscopy support, F. Beck for help with image processing, E. Conti, H. Kiefer, B. Landwehrmeyer, K. Lindenberg, P. Mittl and L. Toledo-Sherman for discussions and A. Bracher, M. Hipp and E. Sakata for the critical reading of the manuscript. This work has been funded by the CHDI Foundation, the German Federal Ministry of Education and Research (FTLDc 01GI1007A), the German Research Foundation (SFB1279) and the European Commission (grant FP7 GA ERC-2012-SyG_318987–ToPAG). Q.G. is the recipient of postdoctoral fellowships from EMBO (EMBO ALTF 73-2015) and the Alexander von Humboldt Foundation.

Author information

Author notes

    • Qiang Guo
    •  & Bin Huang

    These authors contributed equally to this work.

Affiliations

  1. Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany

    • Qiang Guo
    • , Günter Pfeifer
    • , Wolfgang Baumeister
    •  & Rubén Fernández-Busnadiego
  2. Department of Gene Therapy, Ulm University, 89081 Ulm, Germany

    • Bin Huang
    • , Manuel Seefelder
    • , Tatjana Engler
    •  & Stefan Kochanek
  3. Gene Center, Department of Biochemistry and Center for Integrated Protein Science Munich, Ludwig-Maximilians University, 81377 Munich, Germany

    • Jingdong Cheng
  4. Department of Neurology, Ulm University, 89081 Ulm, Germany

    • Patrick Oeckl
    •  & Markus Otto
  5. Department of Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riß, Germany

    • Franziska Moser
    • , Melanie Maurer
    •  & Alexander Pautsch

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Contributions

Q.G., B.H., P.O., A.P., W.B., R.F.-B. and S.K. designed experiments. F.M., M.M. and A.P. performed differential scanning fluorimetry studies. P.O. performed mass spectrometry analyses. B.H. prepared the HTT–HAP40 samples for cryo-EM and performed the majority of the biochemical work together with T.E. M.S. performed the experiments with truncated HAP40 constructs. Q.G. performed the majority of the cryo-EM work. Q.G. and G.P. optimized sample conditions for cryo-EM. J.C. built the atomic model. Q.G., J.C. and R.F.-B. analysed the structure. Q.G., B.H., J.C., M.S., P.O., M.O., A.P., R.F.-B. and S.K. analysed the data. Q.G. and B.H. prepared the figures. Q.G., B.H., W.B., R.F.-B. and S.K. wrote the manuscript. All authors commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Wolfgang Baumeister or Rubén Fernández-Busnadiego or Stefan Kochanek.

Reviewer Information Nature thanks S. Scheres and R. Wetzel for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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    This file contains the uncropped scans with size marker indications.

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https://doi.org/10.1038/nature25502

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