Insect cuticle is composed of proteins and chitin. The cuticular proteins seem to be specific to the type of cuticle (flexible or stiff) that occur at stages of the insect development. The proteins found in the flexible cuticle of larva and pupa of different insects share a conserved C-terminal section [1]; such a region is also found in the soft endocuticle of adults insects [2] as well as in other cuticular proteins including in arachnids [3]. This conserved motif of 35-36 amino acids is known as the R&R consensus since it was first recognized by Rebers and Riddiford. N-terminal to the consensus is a region of hydrophilic amino acids. The two regions together have been called the extended R&R consensus and form an about 70 amino acids chitin-binding domain [4,5].

The R&R chitin-binding domain has been proposed to constitute antiparallel β-pleaated sheets [6].

Some proteins known to contain a R&R chitin-binding domain are listed below:

• Locust cuticle proteins 7 (LM-7), 8 (LM-8), 19 (LM-19) and endocuticle structural glycoprotein ABD-4.
• Hyalophora cecropia cuticle proteins 12 and 66.
• Drosophila larval cuticles proteins I, II, III and IV (LCP1 to LCP4).
• Drosophila pupal cuticle protein (PCP).
• Drosophila pupal cuticle proteins EDG-78E and EDG-84E.
• Manduca sexta cuticle protein LCP-14.
• Tenebrio molitor cuticle proteins ACP-20, A1A, A2B and A3A.
• Araneus diadematus (spider) cuticle proteins ACP 11.9, ACP 12.4, ACP 12.6, ACP 15.5 and ACP 15.7.

We have developed both a pattern and a profile for the R&R chitin-binding domain. The pattern covers the R&R consensus, whereas the profile covers the entire R&R chitin-binding domain.