Remote Homology Between Munc13 MUN Domain and Vesicle Tethering Complexes

J Mol Biol. 2009 Aug 21;391(3):509-17. doi: 10.1016/j.jmb.2009.06.054. Epub 2009 Jun 27.


Most core components of the neurotransmitter release machinery have homologues in other types of intracellular membrane traffic, likely underlying a universal mechanism of intracellular membrane fusion. However, no clear similarity between Munc13s and protein families generally involved in membrane traffic has been reported, despite the essential nature of Munc13s for neurotransmitter release. This crucial function was ascribed to a minimal Munc13 region called the MUN domain, which likely participates in soluble N-ethylmaleimide sensitive factor attachment protein receptor complex (SNARE) assembly and is also found in Ca(2+)-dependent activator protein for secretion. We have now used comparative sequence and structural analyses to study the structure and evolutionary origin of the MUN domain. We found weak yet significant sequence similarities between the MUN domain and a set of protein subunits from several related vesicle tethering complexes, such as Sec6 from the exocyst complex and Vps53 from the Golgi-associated retrograde protein complex. Such an evolutionary relationship allows structure prediction of the MUN domain and suggests functional similarities between MUN domain-containing proteins and multisubunit tethering complexes such as exocyst, conserved oligomeric Golgi complex, Golgi-associated retrograde protein complex, and Dsl1p. These findings further unify the mechanism of neurotransmitter release with those of other types of intracellular membrane traffic and, in turn, support a role for tethering complexes in soluble N-ethylmaleimide sensitive factor attachment protein receptor complex assembly.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport
  • Calcium / metabolism
  • Evolution, Molecular
  • Golgi Apparatus / metabolism
  • Humans
  • Intracellular Membranes / physiology
  • Membrane Fusion
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Neurotransmitter Agents / metabolism
  • Phylogeny
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Sequence Homology, Amino Acid
  • Vesicular Transport Proteins / chemistry
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism


  • Membrane Proteins
  • Multiprotein Complexes
  • Nerve Tissue Proteins
  • Neurotransmitter Agents
  • Protein Subunits
  • Vesicular Transport Proteins
  • Calcium