Beta-1,3-glucan recognition protein-2 (betaGRP-2)from Manduca sexta; an acute-phase protein that binds beta-1,3-glucan and lipoteichoic acid to aggregate fungi and bacteria and stimulate prophenoloxidase activation.

We have isolated and characterized a new beta-1,3-glucan recognition protein that is present in Manduca sexta cuticle and hemolymph. This 52 kDa protein, designated betaGRP-2, is 57% identical in sequence to betaGRP-1 from larval hymolymph of the same insect. BetaGRP-2 differs from betaGRP-1 in its absence of the naive larvae before the wandering stage begins. Transcription of the betaGRP-2 was up-regulated in larvae challenged with yeast or bacteria. BetaGRP-2 contains a region with sequence similarity to several glucanases but lacks glucanase activity. It aggregates yeasts and bacteria to, perhaps, limit the spread of invading cells and ensure a localized defense reaction. BetaGRP-2 binds laminarin and lipoteichoic acid, but not lipopolysaccharide. Laminarin-triggered prophenoloxidase activation was greatly enhanced in the induced larval hemolymph supplemented with purified betaGRP-2. Complementing other studies on pattern recognition molecules in M. sexta, these results indicate that a complex system of protein sensors is an integral component of the insect immune system and that different recognition molecules have overlapping binding specificity and functions.