Death fold

The death fold is a tertiary structure motif commonly found in proteins involved in apoptosis or inflammation-related processes. This motif is commonly found in domains that participate in protein–protein interactions leading to the formation of large functional complexes. Examples of death fold domains include the death domain (DD), death effector domain (DED), Caspase Recruitment Domain (CARD), and pyrin domain (PYD).

Death fold domains are an evolutionarily conserved superfamily of domains that mediate apoptotic signaling. The two types of apoptosis, extrinsic and intrinsic, are tightly regulated by the interplay of activating and inhibitory pathways. The interactions between the four different death fold motifs are a unifying mechanism in both types of apoptosis.

There is a large difference in the primary amino acid sequence of the four different death fold motifs, but each has a similar three-dimensional structure. Death-fold motifs are characterized by six to seven tightly coiled alpha-helices arranged in a "Greek-key" fold. The motifs consist of several defined protein interactions with other suspected apoptotic roles (Lahm).

Caspase recruitment domain (CARD) CARD-containing proteins are found throughout the animal kingdom and may also be present in fungi, plants, and prokaryotes. CARD domains are present on several mammalian procaspases, and have functions in apoptosis, cytokine processing, immune defense, and NF-κB activation. In insects and nematodes, CARDs so far seem restricted to apoptotic proteins.

Death domain (DD) DDs are found primarily in vertebrates (although they are also present in some other animals). DDs are contained on cytokine receptors in the TNF receptor family. DD proteins function in apoptosis and NF-κB signaling in mammals, but only NF-κB signaling Drosophila.

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