Structural basis for the evolutionary inactivation of Ca2+ binding to synaptotagmin 4

Nat Struct Mol Biol. 2004 Sep;11(9):844-9. doi: 10.1038/nsmb817. Epub 2004 Aug 15.

Abstract

The neuronal protein synaptotagmin 1 functions as a Ca(2+) sensor in exocytosis via two Ca(2+)-binding C(2) domains. The very similar synaptotagmin 4, which includes all the predicted Ca(2+)-binding residues in the C(2)B domain but not in the C(2)A domain, is also thought to function as a neuronal Ca(2+) sensor. Here we show that, unexpectedly, both C(2) domains of fly synaptotagmin 4 exhibit Ca(2+)-dependent phospholipid binding, whereas neither C(2) domain of rat synaptotagmin 4 binds Ca(2+) or phospholipids efficiently. Crystallography reveals that changes in the orientations of critical Ca(2+) ligands, and perhaps their flexibility, render the rat synaptotagmin 4 C(2)B domain unable to form full Ca(2+)-binding sites. These results indicate that synaptotagmin 4 is a Ca(2+) sensor in the fly but not in the rat, that the Ca(2+)-binding properties of C(2) domains cannot be reliably predicted from sequence analyses, and that proteins clearly identified as orthologs may nevertheless have markedly different functional properties.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Calcium / chemistry*
  • Calcium / metabolism
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / metabolism
  • Crystallography, X-Ray
  • Evolution, Molecular
  • Exocytosis
  • Glutathione Transferase / metabolism
  • Ligands
  • Lipids / chemistry
  • Magnetic Resonance Spectroscopy
  • Membrane Glycoproteins / chemistry*
  • Membrane Glycoproteins / metabolism
  • Models, Biological
  • Models, Molecular
  • Molecular Sequence Data
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / metabolism
  • Neurons / metabolism
  • Phospholipids / chemistry
  • Protein Binding
  • Protein Structure, Tertiary
  • Rats
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Synaptotagmin I
  • Synaptotagmins

Substances

  • Calcium-Binding Proteins
  • Ligands
  • Lipids
  • Membrane Glycoproteins
  • Nerve Tissue Proteins
  • Phospholipids
  • Recombinant Fusion Proteins
  • Synaptotagmin I
  • Syt1 protein, rat
  • Syt4 protein, rat
  • Synaptotagmins
  • Glutathione Transferase
  • Calcium

Associated data

  • PDB/1W15
  • PDB/1W16