Cingulin-like protein 1, also known as paracingulin or junction-associated-coiled-coil protein (JACOP), is a protein which is encoded by the CGNL1 gene.
The paracingulin polypeptide comprises a globular N-terminal "head" domain and an α-helical C-terminal domain which is presumed to form a coiled-coil dimer. Paracingulin is a paralog of cingulin that arose probably from gene duplication. The CGNL1 gene is conserved among different vertebrate species and has not been so far identified in invertebrates. The homology search highlights that paracingulin and cingulin have 39% identity in the rod tail sequences. They possess also two highly homologous regions in their N-terminus “head” domain including the ZIM region (ZO-1 interaction motif).
The etymology of the name cingulin comes from the Latin "cingere" which means « to form a belt around ». Both, cingulin and paracingulin are localized in the cytoplasmic face of tight junctions (TJ). The prefix « para » refers to “paralog”. However, immunoelectron microscopy indicates that paracingulin is not only localized in the TJ but also in the adherens junctions (AJ) depending on tissue type. TJ and AJ together form the apical junctional complex (AJC) of vertebrate epithelial cells. The proteins present in this complex play a role in many cellular processes i.e., in the adhesion and barrier function of epithelia, the organization and dynamics of the cytoskeleton, as well as the regulation of Rho-GTPase family.
