Nod1/CARD4 is a cytosolic protein structually related to Apaf-1 and plant drug-resistance proteins that has been implicated in apoptosis and inflammatory responses to certain pathogenic bacteria (1-3). It contains an amino-terminal caspase recruitment domain (CARD) that is linked to a central nucleotide-binding domain (NBD; also known as a NOD domain) and is followed by carboxy-terminal leucine-rich repeats (LRR) (1). Like Apaf-1, Nod1 induces apoptosis by a CARD/NBD-dependent activation of caspase-9 (1). The primary function of Nod1 is thought to be as a sensor for certain pathogenic microbes and triggering inflammatory responses including the activation of NF-κB and JNK pathways (4-6). The LRR of Nod1 appears to be involved in recognition of microbial components and the CARD domain induces NF-κB activation in cooperation with the CARD containing kinase, RICK/RIP2/CARDIAK (1,5,6). Mutations in Nod1 have been linked increased susceptibility to asthma (7) and inflammatory bowel disease (8).
