A beta 1,3-glucan recognition protein from an insect, Manduca sexta, agglutinates microorganisms and activates the phenoloxidase cascade

Pattern recognition proteins function in innate immune responses by binding to molecules on the surface of invading pathogens and initiating host defe nse reactions. We report the purification and molecular cloning of a cDNA f or a 53-kDa beta 1,3-glucan-recognition protein from the tobacco hornworm, Manduca sexta. This protein is constitutively expressed in fat body and sec reted into hemolymph, The protein contains a region with sequence similarit y to several glucanases, but it lacks glucanase activity. It binds to the s urface of and agglutinates yeast, as well as Gram-negative and Gram-positiv e bacteria. beta 1,3-Glucan-recognition protein in the presence of laminari n, a soluble glucan, stimulated activation of prophenoloxidase in plasma, w hereas laminarin alone did not. These results suggest that beta 1,3-glucan- recognition protein serves as a pattern recognition molecule for beta 1,3-g lucan on the surface of fungal cell walls. After binding to pl,3-glucan, th e protein may interact with a serine protease, leading to the activation of the prophenoloxidase cascade, a pathway in insects for defense against mic robial infection.