Structure and expression of β-1,3-glucan recognition proteins from the ghost moth, Thitarodes pui (Hepialidae), and their response to Beauveria bassiana infection

Beta-1,3-glucan recognition proteins (beta GRPs), as a class of pattern recognition receptors, are involved in activation of the immune response in invertebrates. We cloned two cDNAs encoding putative beta GRPs from larvae of Thitarodes pui, a host species of Ophiocordyceps sinensis with great economic importance in the Tibetan Plateau. The two putative beta GRPs were phylogenetically classified into a novel clade 4, and designated Tp beta GRP-4a and Tp beta GRP-4b, respectively, with calculated molecular masses of 53,265 and 43,991 Da. Both Tp beta GRPs contained a C-terminal domain with sequence similarity to beta-1,3-glucanases but without the glucanase active site. Tp beta GRP-4b markedly differed from other family members including Tp beta GRP-4a in the N-terminal region by a large deletion of similar to 80 amino acid residues. Homology modelings revealed an eight-stranded beta-sandwich fold (beta 1-beta 8) and two beta-strands (only beta 1 and beta 2), respectively, in the N-terminal domains of Tp beta GRP-4a and -4b. Tp beta GRPs showed similar developmental expression patterns in fat body. Tp beta GRP-4a and -4b transcripts were induced highest 3 beta- and 16-fold, respectively, in resistant 8th instar larvae challenged with conidia of entomopathogenic fungus Beauveria bassiana. By contrast, significant reductions in Tp beta GRPs expression were observed in conidia-injected susceptible 6th instar larvae (compared with saline-injected controls), accompanied by production of hyphal bodies in hemolymph. These results suggest that Tp beta GRPs might contribute to host defense against fungal infection, and Tp beta GRP-4b with the unusual deletion of the N-terminal region might have evolved new functions for beta GRP family proteins. (C) 2011 Elsevier Ltd. All rights reserved.