Calcium-dependent phospholipid binding to the C2A domain of a ubiquitous form of double C2 protein (Doc2β)

Toshio Kojima, Mitsunori Fukuda, Jun Aruga, Katsuhiko Mikoshiba

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)


Rabphilin 3A and Doc2α are synaptic vesicle-associated proteins, and are thought to function as Ca2+ sensors in neurotransmitter release. If either rabphilin 3A or Doc2α plays a role in membrane trafficking, like the synaptotagmins, then non-neural forms should be present. Here we describe the isolation of a mouse cDNA which encodes a novel Doc2 homologue (Doc2β) that is present in all tissues. The encoded protein, which is highly homologous to human Doc2α (70% identity), is composed of 412 amino acids with a calculated relative molecular mass (M(r)) of 45,837. The sequence identity is especially high in two C2 domains (74% in C2A and 84% in C2B). Northern and Western blot analyses have shown that Doc2β is expressed in all cell lines and tissues tested. Ca2+-dependent phospholipid binding assaying of recombinant fusion proteins revealed that the single C2A domain, but not the C2B domain, of Doc2β binds phosphatidycholine and phosphatidylserine (2.5:1, w/w) liposomes. The binding is Ca2+-dependent, with an EC50 value of approximately 1 μM and a Hill coefficient of approximately 3, which are comparable to those of synaptotagmins, rabphilin 3A and Doc2α. Our results suggest that Doc2β is involved in constitutive membrane trafficking.

Original languageEnglish
Pages (from-to)671-676
Number of pages6
JournalJournal of Biochemistry
Issue number3
Publication statusPublished - 1996


  • C2 domain
  • Doc2
  • Rabphilin 3A
  • Synaptotagmin


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