Peptidoglycan activation of the proPO-system without a peptidoglycan receptor protein (PGRP)?
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.
Liu
Haipeng
H
Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
Wu
Chenglin
C
Matsuda
Yasuyuki
Y
Kawabata
Shun-Ichiro
S
Lee
Bok Luel
BL
Söderhäll
Kenneth
K
Söderhäll
Irene
I
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
D002352:Carrier Proteins; D004792:Enzyme Precursors; D010457:Peptidoglycan; D011994:Recombinant Proteins; C118897:peptidoglycan recognition protein; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D057057:Serine Proteases