B-1,3-Glucan recognition protein-2 (βGRP-2) from Manduca sexta:: an acute-phase protein that binds β-1,3-glucan and lipoteichoic acid to aggregate fungi and bacteria and stimulate prophenoloxidase activation

We have isolated and characterized a new 4,3-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 hemolymph of the same insect. betaGRP-2 differs from betaGRP-1 in its absence in the naive larvae before the wandering stage begins. Transcription of the betaGRP-2 gene 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 the 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. (C) 2003 Elsevier Ltd. All rights reserved.