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

Elife. 2014 Oct 10;3:e03648. doi: 10.7554/eLife.03648.

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 Caenorhabditis 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 µ-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.

Keywords: AP2; FCHo proteins; SGIP1; cell biology; clathrin adaptor complex; elegans; endocytosis; protein conformation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Protein Complex 2 / chemistry*
  • Adaptor Protein Complex 2 / genetics
  • Adaptor Protein Complex 2 / metabolism
  • Allosteric Regulation
  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Biological Transport
  • Caenorhabditis elegans / genetics*
  • Caenorhabditis elegans / metabolism
  • Caenorhabditis elegans Proteins / chemistry*
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Clathrin-Coated Vesicles / metabolism
  • Clathrin-Coated Vesicles / ultrastructure
  • Coated Pits, Cell-Membrane / metabolism
  • Coated Pits, Cell-Membrane / ultrastructure
  • Endocytosis / genetics*
  • Gene Expression Regulation
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry*
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Sequence Alignment
  • Signal Transduction

Substances

  • Adaptor Protein Complex 2
  • Caenorhabditis elegans Proteins
  • Carrier Proteins
  • Membrane Proteins
  • Protein Subunits