PROSITE documentation PDOC51258
Munc13-homology domains 1 and 2 (MHD1 and MHD2) profiles


Munc13 proteins constitute a family of three highly homologous molecules (Munc13-1, Munc13-2 and Munc13-3) with homology to Caenorhabditis elegans unc-13p. Munc13 proteins contain a phorbol ester-binding C1 domain (see <PDOC00379>) and two C2 domains, which are Ca2+/phospholipid binding domains (see <PDOC00380>). Sequence analyses have uncovered two regions called Munc13 homology domains 1 (MHD1) and 2 (MHD2) that are arranged between two flanking C2 domains. MHD1 and MHD2 domains are present in a wide variety of proteins from Arabidopsis thaliana, C. elegans, Drosophila melanogaster, mouse, rat and human, some of which may function in a Munc13-like manner to regulate membrane trafficking [1].

The MHD1 and MHD2 domains are predicted to be α-helical [2].

Some proteins known to contain MHD1 and MHD2 domains are listed below:

  • Mammalian Munc13-1. It is specifically targeted to presynaptic active zones and has a central priming function in synaptic vesicle exocytosis from glutaminergic synapses.
  • Mammalian Munc13-2. It plays a role in vesicle maturation during exocytosis as a target of the diacylglycerol second messenger pathway.
  • Mammalian Munc13-3. It probably plays a role in vesicle maturation during exocytosis as a target of the diacylglycerol second messenger pathway.
  • Mammalian Munc13-4. It is predominantly expressed in lung where it is localized to goblet cells of the bronchial epithelium and to alveolar type II cells, both of which are cell types with secretory function.
  • Caenorhabditis elegans unc-13p. It may form part of a signal transduction pathway, transducing the signal from diacylglycerol to effector functions.
  • Mammalian BAI1-associated protein 3 (BAP3) which exhibit the typical Munc13-like domain structure with two C2 domains flanking the MHD1 and MHD2 domains, but which lack the long N-terminus with the C1 domain.
  • Animal calcium-dependent activator proteins for secretion (CAPSs), regulators of large dense-core vesicle secretion. They contain only a MHD1 domain and are otherwise unrelated to Munc13 proteins.
  • Arabidopsis thaliana hypothetical proteins with MHD1 and MHD2 domains but without C1 and C2 domains.
  • Yeast uncharacterized protein YOR296W, where MHD1 and MHD2 enclose a central C2 domain. YOR296W is presumably involved in bud formation.
  • Fission yeast hypothetical protein C11E3.02c in chromosome I, where MHD1 and MHD2 enclose a central C2 domain.

The profile we developed covers the entire MHD1 and MHD2 domains.

Last update:

October 2006 / First entry.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

MHD1, PS51258; Munc13-homology domain 1 (MHD1) profile  (MATRIX)

MHD2, PS51259; Munc13-homology domain 2 (MHD2) profile  (MATRIX)


1AuthorsKoch H. Hofmann K. Brose N.
TitleDefinition of Munc13-homology-domains and characterization of a novel ubiquitously expressed Munc13 isoform.
SourceBiochem. J. 349:247-253(2000).
PubMed ID10861235

2AuthorsBasu J. Shen N. Dulubova I. Lu J. Guan R. Guryev O. Grishin N.V. Rosenmund C. Rizo J.
TitleA minimal domain responsible for Munc13 activity.
SourceNat. Struct. Mol. Biol. 12:1017-1018(2005).
PubMed ID16228007

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