Evolutionarily conserved multiple C2 domain proteins with two transmembrane regions (MCTPs) and unusual Ca2+ binding properties

Ok Ho Shin, Weiping Hau, Yun Wang, Thomas C. Südhof

Research output: Contribution to journalArticlepeer-review

82 Scopus citations


C2 domains are primarily found in signal transduction proteins such as protein kinase C, which generally contain a single C2 domain, and in membrane trafficking proteins such as synaptotagmins, which generally contain multiple C2 domains. In both classes of proteins, C 2 domains usually regulate the respective protein's function by forming Ca2+-dependent or Ca2+-independent phospholipid complexes. We now describe MCTPs (multiple C2 domain and transmembrane region proteins), a novel family of evolutionarily conserved C2 domain proteins with unusual Ca2+-dependent properties. MCTPs are composed of a variable N-terminal sequence, three C2 domains, two transmembrane regions, and a short C-terminal sequence. The invertebrate organisms Caenorhabditis elegans and Drosophila melanogaster express a single MCTP gene, whereas vertebrates express two MCTP genes (MCTP1 and MCTP2) whose primary transcripts are extensively alternatively spliced. Most of the MCTP sequences, in particular the C2 domains, are highly conserved. All MCTP C2 domains except for the second C2 domain of MCTP2 include a perfect Ca2+/phospholipid-binding consensus sequence. To determine whether the C2 domains of MCTPs actually function as Ca2+/phospholipid-binding modules, we analyzed their Ca2+ and phospholipid binding properties. Surprisingly, we found that none of the three MCTP1 C2 domains interacted with negatively charged or neutral phospholipids in the presence or absence of Ca2+. However, Ca2+ titrations monitored via intrinsic tryptophan fluorescence revealed that all three C2 domains bound Ca2+ in the absence of phospholipids with a high apparent affinity (EC50 of ∼1.3-2.3 μM). Our data thus reveal that MCTPs are evolutionarily conserved C2 domain proteins that are unusual in that the C 2 domains are anchored in the membrane by two closely spaced transmembrane regions and represent Ca2+-binding but not phospholipid-binding modules.

Original languageEnglish (US)
Pages (from-to)1641-1651
Number of pages11
JournalJournal of Biological Chemistry
Issue number2
StatePublished - Jan 14 2005

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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