InterPro domain: IPR037768

C2 domains fold into an 8-standed beta-sandwich that can adopt 2 structural arrangements: type I and type II, distinguished by a circular permutation involving their N- and C-terminal beta strands. Many C2 domains are Ca2+-dependent membrane-targeting modules that bind a wide variety of substances including bind phospholipids, inositol polyphosphates, and intracellular proteins. C2 domains with a calcium binding region have negatively charged residues, primarily aspartates, that serve as ligands for calcium ions. This entry represents the second C2 repeat of copines, C2B, and has a type-I topology. The C2B domains of copine-2, copine-6 and copine-7 have been shown to be responsible for the protein calcium-dependent membrane association [ 1 ].

Copines are a widely distributed class of Ca2+-dependent lipid-binding proteins. Most have a characteristic domain structure: two C2 domains in the N-terminal region and a von Willebrand A (VWA) domain in the C-terminal region. They are potentially involved in membrane trafficking, protein-protein interactions, and perhaps even cell division and growth [ 2 , 3 ]. In plants, they are known as BONZAI proteins [ 4 ]. The copine family in plants may have effects in promoting growth and development in addition to repressing cell death [ 5 , 6 ]. Caenorhabditis elegans copine, also known as Nra1, is Involved in nicotinic acetylcholine receptor (nAChR)-mediated sensitivity to nicotine and levamisole [ 7 ].

1. The second C2-domain of copine-2, copine-6 and copine-7 is responsible for their calcium-dependent membrane association. FEBS J. 282, 3722-36
2. The copines, a novel class of C2 domain-containing, calcium-dependent, phospholipid-binding proteins conserved from Paramecium to humans. J. Biol. Chem. 273, 1393-402
3. Copines: a ubiquitous family of Ca(2+)-dependent phospholipid-binding proteins. Cell. Mol. Life Sci. 59, 1467-77
4. Identification and analysis of copine/BONZAI proteins among evolutionarily diverse plant species. Genome 59, 565-73
5. Plant growth homeostasis is controlled by the Arabidopsis BON1 and BAP1 genes. Genes Dev. 15, 2263-72
6. The BON/CPN gene family represses cell death and promotes cell growth in Arabidopsis. Plant J. 45, 166-79
7. Identification and characterization of novel nicotinic receptor-associated proteins in Caenorhabditis elegans. EMBO J. 24, 2566-78