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 (βGRPs), as a class of pattern recognition receptors, are involved in activation of the immune response in invertebrates. We cloned two cDNAs encoding putative βGRPs from larvae of Thitarodes pui, a host species of Ophiocordyceps sinensis with great economic importance in the Tibetan Plateau. The two putative βGRPs were phylogenetically classified into a novel clade 4, and designated TpβGRP-4a and TpβGRP-4b, respectively, with calculated molecular masses of 53,265 and 43,991 Da. Both TpβGRPs contained a C-terminal domain with sequence similarity to β-1,3-glucanases but without the glucanase active site. TpβGRP-4b markedly differed from other family members including TpβGRP-4a in the N-terminal region by a large deletion of ∼80 amino acid residues. Homology modelings revealed an eight-stranded β-sandwich fold (β1–β8) and two β-strands (only β1 and β2), respectively, in the N-terminal domains of TpβGRP-4a and -4b. TpβGRPs showed similar developmental expression patterns in fat body. TpβGRP-4a and -4b transcripts were induced highest 313- and 16-fold, respectively, in resistant 8th instar larvae challenged with conidia of entomopathogenic fungus Beauveria bassiana. By contrast, significant reductions in TpβGRPs 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 TpβGRPs might contribute to host defense against fungal infection, and TpβGRP-4b with the unusual deletion of the N-terminal region might have evolved new functions for βGRP family proteins.