Structural requirements for alpha-latrotoxin binding and alpha-latrotoxin-stimulated secretion. A study with calcium-independent receptor of alpha-latrotoxin (CIRL) deletion mutants

J Biol Chem. 1999 Feb 5;274(6):3590-6. doi: 10.1074/jbc.274.6.3590.


Stimulation of neurotransmitter release by alpha-latrotoxin requires its binding to the calcium-independent receptor of alpha-latrotoxin (CIRL), an orphan neuronal G protein-coupled receptor. CIRL consists of two noncovalently bound subunits, p85, a heptahelical integral membrane protein, and p120, a large extracellular polypeptide with domains homologous to lectin, olfactomedin, mucin, the secretin receptor family, and a novel structural motif common for large orphan G protein-coupled receptors. The analysis of CIRL deletion mutants indicates that the high affinity alpha-latrotoxin-binding site is located within residues 467-891, which comprise the first transmembrane segment of p85 and the C-terminal half of p120. The N-terminal lectin, olfactomedin, and mucin domains of p120 are not required for the interaction with alpha-latrotoxin. Soluble p120 and all its fragments, which include the 467-770 residues, bind alpha-latrotoxin with low affinity suggesting the importance of membrane-embedded p85 for the stabilization of the complex of the toxin with p120. Two COOH-terminal deletion mutants of CIRL, one with the truncated cytoplasmic domain and the other with only one transmembrane segment left of seven, supported both alpha-latrotoxin-induced calcium uptake in HEK293 cells and alpha-latrotoxin-stimulated secretion when expressed in chromaffin cells, although with a different dose dependence than wild-type CIRL and its N-terminal deletion mutant. Thus the signaling domains of CIRL are not critically important for the stimulation of exocytosis in intact chromaffin cells by alpha-latrotoxin.

Publication types

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

MeSH terms

  • Animals
  • Base Sequence
  • Binding Sites
  • COS Cells
  • Calcium / metabolism*
  • Cell Membrane / metabolism
  • DNA Primers
  • Exocytosis
  • GTP-Binding Proteins / metabolism
  • Mutagenesis
  • Protein Binding
  • Receptors, Peptide / genetics
  • Receptors, Peptide / metabolism*
  • Sequence Deletion
  • Signal Transduction
  • Spider Venoms / chemistry
  • Spider Venoms / metabolism*
  • Spider Venoms / pharmacology


  • DNA Primers
  • Receptors, Peptide
  • Spider Venoms
  • alpha-latrotoxin receptor
  • alpha-latrotoxin
  • GTP-Binding Proteins
  • Calcium