Many insect cuticular proteins include a 35-36 amino acid motif known as the R&R consensus. The extensive conservation of this region led to the suggestion that it functions to bind chitin. Provocatively, it has no sequence similarity to the well-known cysteine-containing chitin-binding domain found in chitinases and some peritrophic membrane proteins. Chitin binding has been shown experimentally for this region [1]. Thus arthropods have two distinct classes of chitin binding proteins, those with the chitin-binding domain found in lectins, chitinases and peritrophic membranes (cysCBD) and those with the cuticular protein chitin-binding domain (non-cysCBD) [1].

1: A conserved domain in arthropod cuticular proteins binds chitin. Rebers JE, Willis JH; Insect Biochem Mol Biol 2001;31:1083-1093. PMID:11520687