Drosophila immunity: analysis of PGRP-SB1 expression, enzymatic activity and function

• Published in: PloS one Vol. 6; no. 2; p. e17231
• Main Authors: Zaidman-Rémy, Anna, Poidevin, Mickael, Hervé, Mireille, Welchman, David P, Paredes, Juan C, Fahlander, Carina, Steiner, Hakan, Mengin-Lecreulx, Dominique, Lemaitre, Bruno
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.02.2011; Public Library of Science (PLoS)
• Subjects: Activation; Analysis; Animals; Animals, Genetically Modified; Antimicrobial peptides; Bacilli; Bacteria; Bacterial infections; Biology; Carbohydrate Sequence; Carrier Proteins - genetics; Carrier Proteins - metabolism; Carrier Proteins - physiology; Cascades; Catalysis; Cell growth; Cell walls; Drosophila; Drosophila - enzymology; Drosophila - genetics; Drosophila - immunology; Drosophila - metabolism; Drosophila melanogaster; Drosophila Proteins - metabolism; Drosophila Proteins - physiology; Enzymatic activity; Enzyme Activation - genetics; Enzyme Activation - immunology; Enzymes; Escherichia coli - metabolism; Fat body; Gene Expression Regulation, Enzymologic; Genetic analysis; Genetic research; Genetics; Genomes; Gram-negative bacteria; Gram-positive bacilli; Gram-positive bacteria; Hemolymph; Homologous recombination; Homology; Immune response; Immune system; Immunity; Immunity, Innate - genetics; Immunity, Innate - physiology; Infections; Insects; Lactobacillus casei - metabolism; Mammals; Models, Biological; Molecular Sequence Data; Myogenic Regulatory Factors - metabolism; Myogenic Regulatory Factors - physiology; Peptides; Peptidoglycan - metabolism; Peptidoglycan recognition proteins; Proteins; Receptor mechanisms; Receptors; Recognition; Redundancy; Regulators; Signal transduction; Signal Transduction - immunology; Signal Transduction - physiology; Signaling; Staphylococcus aureus; Stem cells; Toxicology; Virulence Factors, Bordetella - metabolism
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0017231

Peptidoglycan is an essential and specific component of the bacterial cell wall and therefore is an ideal recognition signature for the immune system. Peptidoglycan recognition proteins (PGRPs) are conserved from insects to mammals and able to bind PGN (non-catalytic PGRPs) and, in some cases, to efficiently degrade it (catalytic PGRPs). In Drosophila, several non-catalytic PGRPs function as selective peptidoglycan receptors upstream of the Toll and Imd pathways, the two major signalling cascades regulating the systemic production of antimicrobial peptides. Recognition PGRPs specifically activate the Toll pathway in response to Lys-type peptidoglycan found in most Gram-positive bacteria and the Imd pathway in response to DAP-type peptidoglycan encountered in Gram-positive bacilli-type bacteria and in Gram-negative bacteria. Catalytic PGRPs on the other hand can potentially reduce the level of immune activation by scavenging peptidoglycan. In accordance with this, PGRP-LB and PGRP-SC1A/B/2 have been shown to act as negative regulators of the Imd pathway. In this study, we report a biochemical and genetic analysis of PGRP-SB1, a catalytic PGRP. Our data show that PGRP-SB1 is abundantly secreted into the hemolymph following Imd pathway activation in the fat body, and exhibits an enzymatic activity towards DAP-type polymeric peptidoglycan. We have generated a PGRP-SB1/2 null mutant by homologous recombination, but its thorough phenotypic analysis did not reveal any immune function, suggesting a subtle role or redundancy of PGRP-SB1/2 with other molecules. Possible immune functions of PGRP-SB1 are discussed.