A short-type peptidoglycan recognition protein from the silkworm: Expression, characterization and involvement in the prophenoloxidase activation pathway

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• 作者：Kangkang Chen^a ; Chen Liu^a ; Yan He^b ; Haobo Jiang^b ; Zhiqiang Lu^a ; ^c ; ^{zhiqiang.lu@nwsuaf.edu.cn" class="auth_mail}
• 关键词：PG and PGRP ; peptidoglycan and its recognition protein ; LPS ; lipopolysaccharide ; DAP ; meso-diaminopimelic acid ; SDS&ndash ; PAGE ; sodium dodecyl sulfate&ndash ; polyacrylamide gel electrophoresis ; PO and proPO ; phenoloxidase and its precursor ; QRT-PCR ; quantitative real-time PCR ; PBS ; phosphate buffered saline ; BSA ; bovine serum albumin
• 刊名：Developmental and Comparative Immunology
• 出版年：July, 2014
• 年：2014
• 卷：45
• 期：1
• 页码：1-9
• 全文大小：2848 K

文摘

Recognition of invading microbes as non-self is the first step of immune responses. In insects, peptidoglycan recognition proteins (PGRPs) detect peptidoglycans (PGs) of bacterial cell wall, leading to the activation of defense responses. Twelve PGRPs have been identified in the silkworm, Bombyx mori, through bioinformatics analysis. However, their biochemical functions are mostly uncharacterized. In this study, we found PGRP-S5 transcript levels were up-regulated in fat body and midgut after bacterial infection. Using recombinant protein isolated from Escherichia coli, we showed that PGRP-S5 binds to PGs from certain bacterial strains and induces bacteria agglutination. Enzyme activity assay confirmed PGRP-S5 is an amidase; we also showed it is an antibacterial protein effective against both Gram-positive and -negative bacteria. Additionally, we demonstrated that specific recognition of PGs by PGRP-S5 is involved in the prophenoloxidase activation pathway. Together, these data suggest the silkworm PGRP-S5 functions as a pattern recognition receptor for the prophenoloxidase pathway initiation and as an effecter to inhibit bacterial growth as well. We finally discussed possible roles of PGRP-S5 as a receptor for antimicrobial peptide gene induction and as an immune modulator in the midgut.