A conserved domain in arthropod cuticular proteins binds chitin

Area of Science:

• Biochemistry
• Molecular Biology
• Entomology

Background:

• Insect cuticles contain numerous proteins, many featuring a conserved 35-36 amino acid R&R consensus motif.
• The function of the R&R consensus in chitin binding has been hypothesized but not definitively proven, especially given its lack of similarity to known chitin-binding domains.

Purpose of the Study:

• To investigate the role of the R&R consensus motif in chitin binding by cuticular proteins.
• To determine if this motif is sufficient for chitin binding and to characterize its distinctness from other chitin-binding domains.

Main Methods:

• Expression of recombinant proteins, including a cuticular protein (AGCP2b) from Anopheles gambiae, in E. coli.
• Purification of recombinant proteins and fusion proteins (e.g., GST-AGCP2b fragment).
• Chitin-binding assays using chitin beads and directed mutagenesis to identify key residues.

Main Results:

• A 65-amino acid region of AGCP2b, containing the R&R consensus, was found to be necessary and sufficient for chitin binding.
• Fusion of this region to glutathione-S-transferase (GST) conferred chitin-binding ability.
• Mutagenesis of conserved residues within the R&R consensus abolished chitin binding.

Conclusions:

• Arthropods possess at least two distinct classes of chitin-binding proteins: those with the cysteine-containing chitin-binding domain (cysCBD) and those with a novel, non-cysteine cuticular protein chitin-binding domain (non-cysCBD) characterized by the R&R consensus.
• The R&R consensus motif represents a novel chitin-binding domain in insect cuticular proteins.