molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

, copines is a name for the group of human proteins that includes members such as CPNE1,

CPNE4 Copine-4 is a protein that in humans is encoded by the ''CPNE4'' gene. Calcium-dependent membrane-binding proteins may regulate molecular events at the interface of the cell membrane and cytoplasm In cell biology, the cytoplasm is all of th ...

, CPNE6, and CPNE8. These are highly conserved, calcium-dependent

membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...

s found in a variety of eukaryotes. The domain structure of these 55 kDa proteins suggests that they may have a role in

membrane trafficking Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory ...

in some prokaryotes as well as eukaryotes. Copines contains two

C2 domains A C2 domain is a protein structural domain involved in targeting proteins to cell membranes. The typical version (PKC-C2) has a beta-sandwich composed of 8 β-strands that co-ordinates two or three calcium ions, which bind in a cavity formed by t ...

which play a role in signal transduction by binding to calcium, phospholipids, or polyphosphates. Both domains are located at the N-terminal portion of the protein which is not the case for most other double C2 domain proteins, and their role is most similar to that carried out by proteins that exhibit a single C2 domain. The core domain located at the C-terminus part of the copine is found to have a unique and conserved primary sequence. The function of the core domain is still uncertain, however, researchers believe it has a similar function to the "A domain" in

integrins Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, ...

. This similarity in function involves serving as a binding site for target proteins, and is supported by evidence that the copine core domain exhibits secondary and tertiary structures comparable to the integrin A domain.

References

Protein families {{protein-stub