A pattern-recognition protein for β-1,3-glucan -: The binding domain and the cDNA cloning of β-1,3-glucan recognition protein from the silkworm, Bombyx mori

The beta-1,S-glucan recognition protein (beta GRP) has strong specific affinity for beta-1,3-glucan, a component of the fungal cell wall. Its interaction with beta-1,3-glucan initiates the activation of the prophenoloxidase cascade, which is an important defense system in invertebrates of many species. We cloned the cDNA of the beta GRP of the silkworm Bombyx mori. The beta GRP mRNA transcript was constitutively expressed in the hemocytes, fat body, and epithelial cells of the naive silkworm. At the same time, a bacterial or yeast challenge was indicated to intensify the transcription, Comparison of the deduced amino acid sequence with known sequences revealed that the beta GRP contained a region (Thr(264) to Pro(386)) displaying significant similarity to the catalytic regions of bacterial beta-1,3-glucanases and much higher similarity to the glucanase-like regions of Gram-negative bacteria-binding proteins found in the silkworm B, mori and the mosquito Anopheles gambiae, The region (Thr(264) to Pro(386)) Of the beta GRP, however, was demonstrated not to have appreciable affinity for beta-1,3-glucan. A recombinant peptide corresponding to an N-terminal region (Tyr(1) to Ala(102)) of the beta GRP bound strongly to beta-1,3-glucan. These results indicate that the binding domain of the beta GRP for beta-1,3-glucan is located in the N-terminal region. Glucanases and the current pattern-recognition proteins that contain a glucanase-like region seem to have a common origin in their molecular evolution.