CARD11

Caspase recruitment domain-containing protein 11 also known as CARD-containing MAGUK protein 1 (Carma 1) is a protein in the CARD-CC protein family that in humans is encoded by the CARD11 gene. CARD 11 is a membrane associated protein that is found in various human tissues, including the thymus, spleen, liver, and peripheral blood leukocytes. Similarly, CARD 11 is also found in abundance in various lines of cancer cells.

Function
The protein encoded by this gene belongs to the membrane-associated guanylate kinase (MAGUK) family, a class of proteins that functions as molecular scaffolds for the assembly of multiprotein complexes at specialized regions of the plasma membrane. This protein is also a member of the CARD protein family, which is defined by carrying a characteristic caspase-associated recruitment domain (CARD). CARD11 (CARMA1) has a domain structure similar to that of CARD10 (CARMA3) and CARD14 (CARMA2) as a member of the CARD-CC family with a C terminal MAGUK domain (the so-called CARMA proteins). The CARD domain of proteins in the CARD-CC family have been shown to specifically interact with BCL10, a protein known to function as a positive regulator of NF-κB activation by recruitment and activation of MALT1. When overexpressed in cells, this protein family activates NF-κB and induces the phosphorylation of BCL10.

CARD11 is critical for T cell and B cell function and is activated after T cell receptor or B cell receptor stimulation. After receptor stimulation, CARD11 is phosphorylated by PKC-θ (in T cells) or PKC-β (in B cells). The phosphorylation induces formation of filamentous CARD11 multimers that recruit BCL10 and MALT1, which in turn activates NF-κB. Loss of function mutations in CARD11 cause severe combined immunodeficiency (SCID) since the function of cells critical for adaptive immunity are disrupted.

Structure
The structure of CARD11 involves multiple domains that impact the protein's ability to activate BCL10 and NF-κB activity. CARD11 has a CARD domain, a serine-threonine rich region, is associated with the N-terminus, which is essential for NF-κB signaling activity. The region following the CARD domain is highly coiled. In deleting the CARD domain, all NF-κB signaling activity was prevented. The CARD domain on CARD11 interacts with the CARD domain on BCL10 to initiate the signaling pathway.

On the C-terminus of CARD11 there is the MAGUK domain that is associated with the cell membrane. This domain is often referred to as the inhibitory domain. Protein kinase C activates CARD11 by phosphorylating serine residues within the inhibitory domain.

Interactions
CARD11 has been shown to interact with BCL10. This interaction occurs between the CARD domain on BCL10 and the CARD domain on CARD11, and results in signal propagation and NF-κB activation.