Essential role of Ca2+/calmodulin in Early Endosome Antigen-1 localization

Mol Biol Cell. 2003 Jul;14(7):2935-45. doi: 10.1091/mbc.e02-09-0591. Epub 2003 Mar 20.


Ca2+ is an essential requirement in membrane fusion, acting through binding proteins such as calmodulin (CaM). Ca2+/CaM is required for early endosome fusion in vitro, however, the molecular basis for this requirement is unknown. An additional requirement for endosome fusion is the protein Early Endosome Antigen 1 (EEA1), and its recruitment to the endosome depends on phosphatidylinositol 3-phosphate [PI(3)P] and the Rab5 GTPase. Herein, we demonstrate that inhibition of Ca2+/CaM, by using either chemical inhibitors or specific antibodies directed to CaM, results in a profound inhibition of EEA1 binding to endosomal membranes both in live cells and in vitro. The concentration of Ca2+/CaM inhibitors required for a full dissociation of EEA1 from endosomal membranes had no effect on the activity of phosphatidylinositol 3-kinases or on endogenous levels of PI(3)P. However, the interaction of EEA1 with liposomes containing PI(3)P was decreased by Ca2+/CaM inhibitors. Thus, Ca2+/CaM seems to be required for the stable interaction of EEA1 with endosomal PI(3)P, perhaps by directly or indirectly stabilizing the quaternary organization of the C-terminal FYVE domain of EEA1. This requirement is likely to underlie at least in part the essential role of Ca2+/CaM in endosome fusion.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Animals
  • COS Cells
  • Calcium / metabolism
  • Calmodulin / antagonists & inhibitors
  • Calmodulin / metabolism*
  • Calmodulin / physiology
  • Chlorocebus aethiops
  • Endosomes / metabolism
  • Endosomes / physiology
  • Liposomes
  • Membrane Fusion* / physiology
  • Membrane Proteins / metabolism*
  • Membrane Proteins / physiology
  • Microscopy, Fluorescence
  • Mutation
  • Phosphatidylinositol 3-Kinases / metabolism
  • Protein Structure, Quaternary / physiology
  • Recombinant Proteins / metabolism
  • Sulfonamides / pharmacology
  • Vesicular Transport Proteins
  • rab5 GTP-Binding Proteins / metabolism


  • Calmodulin
  • Liposomes
  • Membrane Proteins
  • Recombinant Proteins
  • Sulfonamides
  • Vesicular Transport Proteins
  • early endosome antigen 1
  • N-(6-aminohexyl)-1-naphthalenesulfonamide
  • rab5 GTP-Binding Proteins
  • Calcium