A β1,3-Glucan Recognition Protein from an Insect, Manduca sexta, Agglutinates Microorganisms and Activates the Phenoloxidase Cascade

Abstract

Pattern recognition proteins function in innate immune responses by binding to molecules on the surface of invading pathogens and initiating host defense reactions. We report the purification and molecular cloning of a cDNA for a 53-kDa ␤1,3-glucan-recognition protein from the tobacco hornworm, Manduca sexta. This protein is constitutively expressed in fat body and secreted into hemolymph. The protein contains a region with sequence similarity to several glucanases, but it lacks glucanase activity. It binds to the surface of and agglutinates yeast, as well as Gram-negative and Gram-positive bacteria. ␤1,3-Glucan-recognition protein in the presence of laminarin, a soluble glucan, stimulated activation of prophenoloxidase in plasma, whereas laminarin alone did not. These results suggest that ␤1,3-glucan-recognition protein serves as a pattern recognition molecule for ␤1,3-glucan on the surface of fungal cell walls. After binding to ␤1,3-glucan, the protein may interact with a serine protease, leading to the activation of the prophenoloxidase cascade, a pathway in insects for defense against microbial infection.

Eicosanoids mediate Manduca sexta cellular response to the fungal pathogen Beauveria bassiana: A role for the lipoxygenase pathway

“…Immulectin-1 binds both bacteria and yeast, while immulectin-2 is LPS-specific (Yu et al, 1999;Yu and Kanost, 2000). A lectin in M. sexta that binds the (b1,3-glucans recognizes fungal infections (Ma and Kanost 2000). It is likely that M. sexta also has pattern recognition receptor for peptidoglycan, as does Bombyx mori (Ochiai and Ashida, 1999).…”

An Ancient Enzyme Domain Hidden in the Putative β-Glucan Elicitor Receptor of Soybean May Play an Active Part in the Perception of Pathogen-associated Molecular Patterns during Broad Host Resistance

“…Linear 1,3-␤-glucans represent molecular patterns specific for fungi, which, after binding to the ␤GRPs, lead to the activation of insect-specific defense pathways, i.e. the prophenoloxidase pathway or the induction of antimicrobial peptide genes (57,58). ␤GRPs and the GBPs from plants share other properties also.…”

Characterization and Properties of a 1,3-β-d-Glucan Pattern Recognition Protein of Tenebrio molitor Larvae That Is Specifically Degraded by Serine Protease during Prophenoloxidase Activation

“…The proPO activation pathway, like the vertebrate complement system, is a proteolytic cascade containing several serine proteases and their inhibitors and terminates with the zymogen, proPO. Microbial carbohydrates such as LPS, PGN, or 1,3-D-␤-glucan will first react with pattern recognition proteins, which then will induce activation of several serine proteases within the proPO system (7)(8)(9)(10)(11)(12). It is known that one of the serine proteases in the cascade, which is named proPO-activating enzyme or factor, will cleave proPO to generate the active enzyme, phenoloxidase (PO) (13)(14)(15)(16).…”