ApiLoc - A database of published protein sub-cellular localisation in Apicomplexa

version 3 (curated until May 28, 2011)

Identification and characterization of an escorter for two secretory adhesins in Toxoplasma gondii.

Reiss, M., Viebig, N., Brecht, S., Fourmaux, M. N., Soete, M., Di Cristina, M., Dubremetz, J. F., Soldati, D. (2001 Feb 5, J Cell Biol)

The intracellular protozoan parasite Toxoplasma gondii shares with other members of the Apicomplexa a common set of apical structures involved in host cell invasion. Micronemes are apical secretory organelles releasing their contents upon contact with host cells. We have identified a transmembrane micronemal protein MIC6, which functions as an escorter for the accurate targeting of two soluble proteins MIC1 and MIC4 to the micronemes. Disruption of MIC1, MIC4, and MIC6 genes allowed us to precisely dissect their contribution in sorting processes. We have mapped domains on these proteins that determine complex formation and targeting to the organelle. MIC6 carries a sorting signal(s) in its cytoplasmic tail whereas its association with MIC1 involves a lumenal EGF-like domain. MIC4 binds directly to MIC1 and behaves as a passive cargo molecule. In contrast, MIC1 is linked to a quality control system and is absolutely required for the complex to leave the early compartments of the secretory pathway. MIC1 and MIC4 bind to host cells, and the existence of such a complex provides a plausible mechanism explaining how soluble adhesins act. We hypothesize that during invasion, MIC6 along with adhesins establishes a bridge between the host cell and the parasite.

PubMed: 11157983, full text

Localisation information

TGME49_091890 (MIC1, Mic 1) microneme protein MIC1

Experimental localisation: microneme during tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "In wild-type parasites, T101F7 mAb anti-MIC1 and polyclonal anti-MIC4 showed perfect colocalization of the two proteins and a typical apical micronemes staining."
  • Microscopy type: Light
  • Microscopy method: Monoclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: Blast from CAA96466 from 9027753 annotation matches
  • Localisation record: microneme during tachyzoite

TGME49_008030 (MIC4, MIC 4) microneme protein MIC4

Experimental localisation: microneme during tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "In wild-type parasites, T101F7 mAb anti-MIC1 and polyclonal anti-MIC4 showed perfect colocalization of the two proteins and a typical apical micronemes staining"
  • Microscopy type: Light, EM
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: inferred from another publication
  • Localisation record: microneme during tachyzoite

TGME49_018520 (MIC6) microneme protein MIC6

Experimental localisation: microneme during tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "We have identified a transmembrane micronemal protein MIC6, which functions as an escorter for the accurate targeting of two soluble proteins MIC1 and MIC4 to the micronemes."
  • Microscopy type: Light and EM
  • Microscopy method: antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: Blast from AAD28185, annotation matches
  • Localisation record: microneme during tachyzoite
  • Comment: disruption of TgMIC6 results in mistrafficking of TgMIC4 and TgMIC1 to dense granules, the “default” secretory pathway

TGME49_033460 (SAG1, SRS29B, P30/SAG1, BSR4, P30) SRS29B (= SAG1, P30)

Experimental localisation: parasite plasma membrane during tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "SAG1TM-CDMIC6 accumulates precisely in the micronemes as demonstrated by immunoelectron microscopy using anti-SAG1 antibodies. SAG1 is detected by gold particles and, when GPI anchored, was found in its normal location at the parasite surface (arrowheads)."
  • Microscopy type: Light
  • Microscopy method: antibody
  • Strain: RH
  • Gene model mapping comments: Blast from EF585681.1, annotation matches
  • Localisation record: surface during tachyzoite