O. rhinoceros defensin and scarabaecin are antimicrobial peptides isolated from the coconut rhinoceros beetle, Oryctes rhinoceros. Scarabaecin shows both antifungal and antibacterial activity whereas O. r. defensin shows only antibacterial activity. Scarabaecin binds to chitin but not to curdlan or peptidoglycan. Although action mechanism of scarabaecin is not known, its binding activity to chitin is reasonable for its antifungal activity. Scarabaecin shows homology with a putative chitin binding domain of horseshoe crab antibacterial peptide, tachycitin. The functional domain might be conserved through evolution. O. r. defensin also shows chitin binding activity although it does not have antifungal activity and shows no homology with other chitin binding proteins. Biological significance of the chitin binding activity might be attributed to accumulation around wound where exoskeletal chitin is exposed to hemolymph to prepare against microbial infection. Defensin binds to peptidoglycan that is widely distributed as a bacterial cell wall component. As bacterial membrane is assumed to be a target of defensin, its binding activity to peptidoglycan may be important for the antibacterial activity.
Species 1: Coleoptera Scarabaeidae Oryctes rhinoceros (coconut rhinoceros beetle)
Keywords: chitin binding, antimicrobial peptide
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