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. It contains an amino-terminal caspase recruitment domain that is linked to a central nucleotide-binding domain and is followed by carboxy-terminal leucine-rich repeats. Like Apaf-1, Nod1 induces apoptosis by a CARD/NBD-dependent activation of caspase-9. 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. 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. Mutations in Nod1 have been linked increased susceptibility to asthma and inflammatory bowel disease.
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