The membrane-associated proteins FCHo and SGIP are allosteric activators of the AP2 clathrin adaptor complex

  1. Gunther Hollopeter
  2. Jeffrey J Lange
  3. Ying Zhang
  4. Thien N Vu
  5. Mingyu Gu
  6. Michael Ailion
  7. Eric J Lambie
  8. Brian D Slaughter
  9. Jay R Unruh
  10. Laurence Florens
  11. Erik M Jorgensen  Is a corresponding author
  1. Stowers Institute for Medical Research, United States
  2. Howard Hughes Medical Institute, University of Utah, United States
  3. University of Utah, United States
  4. University of Washington, United States
  5. Ludwig-Maximilians-University, Germany

Abstract

The AP2 clathrin adaptor complex links protein cargo to the endocytic machinery but it is unclear how AP2 is activated on the plasma membrane. Here we demonstrate that the membrane-associated proteins FCHo and SGIP1 convert AP2 into an open, active conformation. We screened for C. elegans mutants that phenocopy the loss of AP2 subunits and found that AP2 remains inactive in fcho-1 mutants. A subsequent screen for bypass suppressors of fcho-1 nulls identified 71 compensatory mutations in all four AP2 subunits. Using a protease-sensitivity assay we show that these mutations restore the open conformation in vivo. The domain of FCHo that induces this rearrangement is not the F-BAR domain or the mu-homology domain, but rather is an uncharacterized 90 amino acid motif, found in both FCHo and SGIP proteins, that directly binds AP2. Thus, these proteins stabilize nascent endocytic pits by exposing membrane and cargo binding sites on AP2.

Article and author information

Author details

  1. Gunther Hollopeter

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Jeffrey J Lange

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Ying Zhang

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Thien N Vu

    Howard Hughes Medical Institute, University of Utah, Salt Lake City, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Mingyu Gu

    University of Utah, Salt Lake City, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Michael Ailion

    University of Washington, Seattle, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. Eric J Lambie

    Ludwig-Maximilians-University, Munich, Germany
    Competing interests
    The authors declare that no competing interests exist.
  8. Brian D Slaughter

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  9. Jay R Unruh

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  10. Laurence Florens

    Stowers Institute for Medical Research, Kansas City, United States
    Competing interests
    The authors declare that no competing interests exist.
  11. Erik M Jorgensen

    Howard Hughes Medical Institute, University of Utah, Salt Lake City, United States
    For correspondence
    jorgensen@biology.utah.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Suzanne R Pfeffer, Stanford University, United States

Publication history

  1. Received: June 10, 2014
  2. Accepted: October 1, 2014
  3. Accepted Manuscript published: October 10, 2014 (version 1)
  4. Version of Record published: November 3, 2014 (version 2)

Copyright

© 2014, Hollopeter et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Gunther Hollopeter
  2. Jeffrey J Lange
  3. Ying Zhang
  4. Thien N Vu
  5. Mingyu Gu
  6. Michael Ailion
  7. Eric J Lambie
  8. Brian D Slaughter
  9. Jay R Unruh
  10. Laurence Florens
  11. Erik M Jorgensen
(2014)
The membrane-associated proteins FCHo and SGIP are allosteric activators of the AP2 clathrin adaptor complex
eLife 3:e03648.
https://doi.org/10.7554/eLife.03648
  1. Further reading

Further reading

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    Research Article Updated

    Clathrin-mediated endocytosis is an evolutionarily ancient membrane transport system regulating cellular receptivity and responsiveness. Plasmalemma clathrin-coated structures range from unitary domed assemblies to expansive planar constructions with internal or flanking invaginated buds. Precisely how these morphologically-distinct coats are formed, and whether all are functionally equivalent for selective cargo internalization is still disputed. We have disrupted the genes encoding a set of early arriving clathrin-coat constituents, FCHO1 and FCHO2, in HeLa cells. Endocytic coats do not disappear in this genetic background; rather clustered planar lattices predominate and endocytosis slows, but does not cease. The central linker of FCHO proteins acts as an allosteric regulator of the prime endocytic adaptor, AP-2. By loading AP-2 onto the plasma membrane, FCHO proteins provide a parallel pathway for AP-2 activation and clathrin-coat fabrication. Further, the steady-state morphology of clathrin-coated structures appears to be a manifestation of the availability of the muniscin linker during lattice polymerization.

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    During cell division, kinetochore microtubules (KMTs) provide a physical linkage between the chromosomes and the rest of the spindle. KMTs in mammalian cells are organized into bundles, so-called kinetochore-fibers (k-fibers), but the ultrastructure of these fibers is currently not well characterized. Here, we show by large-scale electron tomography that each k-fiber in HeLa cells in metaphase is composed of approximately nine KMTs, only half of which reach the spindle pole. Our comprehensive reconstructions allowed us to analyze the three-dimensional (3D) morphology of k-fibers and their surrounding MTs in detail. We found that k-fibers exhibit remarkable variation in circumference and KMT density along their length, with the pole-proximal side showing a broadening. Extending our structural analysis then to other MTs in the spindle, we further observed that the association of KMTs with non-KMTs predominantly occurs in the spindle pole regions. Our 3D reconstructions have implications for KMT growth and k-fiber self-organization models as covered in a parallel publication applying complementary live-cell imaging in combination with biophysical modeling (Conway et al., 2022). Finally, we also introduce a new visualization tool allowing an interactive display of our 3D spindle data that will serve as a resource for further structural studies on mitosis in human cells.