This domain is called the Peritrophin-A domain and is found in chitin binding proteins particularly peritrophic matrix proteins of insects and animal chitinases. Copies of the domain are also found in some baculoviruses. Relevant references that describe proteins with this domain include [1-3]. It is an extracellular domain that contains six conserved cysteines that probably form three disulphide bridges. Chitin binding has been demonstrated for a protein containing only two of these domains [1].

1: A type I peritrophic matrix protein from the malaria vector Anopheles gambiae binds to chitin. Cloning, expression, and characterization. Shen Z, Jacobs-Lorena M; J Biol Chem 1998;273:17665-17670. PMID:9651363

2: Characterization of a major peritrophic membrane protein, peritrophin-44, from the larvae of Lucilia cuprina. cDNA and deduced amino acid sequences. Elvin CM, Vuocolo T, Pearson RD, East IJ, Riding GA, Eisemann CH, Tellam RL; J Biol Chem 1996;271:8925-8935. PMID:8621536

3: Antibody-mediated inhibition of the growth of larvae from an insect causing cutaneous myiasis in a mammalian host. Casu R, Eisemann C, Pearson R, Riding G, East I, Donaldson A, Cadogan L, Tellam R; Proc Natl Acad Sci U S A 1997;94:8939-8944. PMID:9256413