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. 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.