Antifungal defense in termite nests by a pattern recognition protein with β-(1,3)-glucanase activity

Pattern recognition proteins of the innate immune system are critical for protecting insects from pathogens. Gram-negative-bacteria binding proteins (GNBPs) and peptidoglycan recognition proteins (PGRPs), two classes of pattern recognition proteins, appear to have evolved from ancient homeostatic enzymes. We have recently found that termite GNBPs, unlike other insect GNBPs, have retained β-(1,3)-glucanase activity, and function as broad-range pattern recognition receptors with direct antifungal activity. This dual function protein is toxic to the fungal pathogen Metarhizium anisopliae and protects termites (Nasutitermes corniger) from infection in-vivo. Furthermore, small toxic molecules (defensins and/or other small antifungals) appear to work synergistically with GNBPs, possibly because the enzyme activity of termite GNBPs disrupts the fungal cell wall allowing small effectors to access the cell. Remarkably, GNBPs are incorporated into nest building material and provide a potential external immune sensor/effector system. Termites therefore appear to have co-opted components of the internal immune system for external defense.