The Copines, a Novel Class of C2 Domain-containing, Calciumdependent, Phospholipid-binding Proteins Conserved from Paramecium to Humans

Abstract

In an attempt to identify proteins that might underlie membrane trafficking processes in ciliates, calcium-dependent, phospholipid-binding proteins were isolated from extracts of Paramecium tetraurelia. The major protein obtained, named copine, had a mass of 55 kDa, bound phosphatidylserine but not phosphatidylcholine at micromolar levels of calcium but not magnesium, and promoted lipid vesicle aggregation. The sequence of a 920-base pair partial cDNA revealed that copine is a novel protein that contains a C2 domain likely to be responsible for its membrane active properties. Paramecium was found to have two closely related copine genes, CPN1 and CPN2. Current sequence data bases indicate the presence of multiple copine homologs in green plants, nematodes, and humans. The full-length sequences reveal that copines consist of two C2 domains at the N terminus followed by a domain similar to the A domain that mediates interactions between integrins and extracellular ligands. A human homolog, copine I, was expressed in bacteria as a fusion protein with glutathione S-transferase. This recombinant protein exhibited calcium-dependent phospholipid binding properties similar to those of Paramecium copine. An antiserum raised against a fragment of human copine I was used to identify chromobindin 17, a secretory vesicle-binding protein, as a copine. This association with secretory vesicles, as well the general ability of copines to bind phospholipid bilayers in a calcium-dependent manner, suggests that these proteins may function in membrane trafficking.

Copine-I represses NF-κB transcription by endoproteolysis of p65

“…The copine-I AD was the most effective inhibitor of p65 transcription. This result is consistent with the vWA being the functional domain of the copine-I protein (Creutz et al, 1998). The inability of the Myr-copine-I construct to block NFkB-responsive luciferase reporter suggests that membrane localization of copine-I disrupts the ability of copine-I to inhibit NF-kB activity.…”

“…Secondary structure predictions and crystal structure data of the vWF indicate that the AD is composed of alternating a-helices and b-strands that adopt a classic a/b Rossmann fold. Similar to many vWA-containing proteins, copine contains a metal ion-dependent adhesion site (MIDAS) motif, which is critical for manganese and magnesium binding (Creutz et al, 1998;Tomsig and Creutz, 2000).…”

Copine-III interacts with ErbB2 and promotes tumor cell migration

“…Copine-III is a Ca 2 þ -dependent, membrane-binding protein Copine-III belongs to a family of proteins, which have been shown to be Ca 2 þ -dependent, phospholipid binders (Creutz et al, 1998;Tomsig et al, 2003). Copine-III is ubiquitously expressed in human tissues (HUGE database); however, essentially nothing is known about its role in normal or cancer tissue.…”

Identification and functional clustering of global gene expression differences between age-related cataract and clear human lenses and aged human lenses

“…The actin-based cytoskeleton has been shown to interact with epithelial sodium channels, sodium/potassium/ chloride co-transporters and sodium/potassium ATPase and is therefore likely to be involved in alterations in ionic transporters. Copine III is another gene involved in membrane trafficking processes (Creutz et al, 1998) upon calcium binding. We have detected that Copine III is increased in cataracts relative to clear lenses by 7-fold.…”