title: Peptidoglycan activation of the proPO-system without a peptidoglycan receptor protein (PGRP)?
abstract: Recognition of microbial polysaccharide by pattern recognition receptors triggers the prophenoloxidase (proPO) cascade, resulting in melanin synthesis and its deposition on the surface of invading pathogens. Several masquerade-like proteins and serine proteinase homologues have been shown to be involved in the proPO activation in insects. In this study, a novel serine proteinase homologue, Pl-SPH2, was found and isolated as a 30kDa protein from hemocytes of the freshwater crayfish, Pacifastacus leniusculus, by its binding property to a partially lysozyme digested or TCA-treated insoluble Lysine (Lys)-type peptidoglycan (PGN) and soluble polymeric Lys-type PGN. Two other proteins, the Pl-SPH1 and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) were also found in the several different PGN-binding assays. However no PGRP homologue was detected. Neither was any putative PGRP found after searching available crustacean sequence databases. If RNA interference of Pl-SPH2, Pl-SPH1 or LGBP in the crayfish hematopoietic tissue cell culture was performed, it resulted in lower PO activity following activation of the proPO-system by soluble Lys-type PGN. Taken together, we report for the first time that Lys-type PGN is a trigger of proPO-system activation in a crustacean and that two Pl-SPHs are involved in this activation possibly by forming a complex with LGBP and without a PGRP.
authors: Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
authors: Haipeng
authors: H
authors: Liu
authors: Chenglin
authors: C
authors: Wu
authors: Yasuyuki
authors: Y
authors: Matsuda
authors: Shun-Ichiro
authors: S
authors: Kawabata
authors: Bok Luel
authors: BL
authors: Lee
authors: Kenneth
authors: K
authors: Söderhäll
authors: Irene
authors: I
authors: Söderhäll
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003400:Astacoidea / Q000145:classification / Q000235:genetics / Q000276:immunology; D016367:Baculoviridae / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000276:immunology*; D004156:Catechol Oxidase / Q000276:immunology*; D002478:Cells, Cultured; D004792:Enzyme Precursors / Q000276:immunology*; D005786:Gene Expression Regulation; D007113:Immunity, Innate; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics; D057057:Serine Proteases / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D015854:Up-Regulation
chemical_list: D002352:Carrier Proteins; D004792:Enzyme Precursors; D010457:Peptidoglycan; D011994:Recombinant Proteins; C118897:peptidoglycan recognition protein; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D057057:Serine Proteases