Abstract
Peptidoglycan recognition proteins (PGRPs) are innate immune molecules that have been structurally conserved throughout evolution in invertebrates and vertebrates. In this study, peptidoglycan recognition protein HcPGRP1 and its isoform HcPGRP1a were identified in the freshwater mussel Hyriopsis cumingii. The full-length cDNAs of HcPGRP1 (973 bp) and HcPGRP1a (537 bp) encoded polypeptides with 218 and 151 amino acids, respectively. Sequence analysis showed that HcPGRP1 had one C-terminal PGRP domain that was conserved throughout evolution. Phylogenetic analysis showed that HcPGRP1 clustered closely with EsPGRP4 of Euprymna scolopes. Real-time PCR showed that the mRNA transcripts of HcPGRP1 and HcPGRP1a were constitutively expressed in various tissues, with the highest level in hepatopancreas. Stimulation with lipopolysaccharide (LPS) and peptidoglycan (PGN) significantly up-regulated HcPGRP1 mRNA expression in hepatopancreas and foot, but not in gill, whereas HcPGRP1a expression was significantly up-regulated in all three tissues. Our results indicate that HcPGRP1 is both a constitutive and inducible protein that may be involved in immune responses (recognition and defense) against invaders.
Highlights
The innate immune system is the first line of defense against invading microorganisms in vertebrates and the only line of defense in invertebrates and plants (Medzhitov and Janeway, 2002; Hoffmann, 2003)
The findings reported here should be useful in understanding the immune significance of Peptidoglycan recognition proteins (PGRPs) in mollusks
Molecular features of HcPGRP1 and HcPGRP1a cDNA The cDNA sequence of H. cumingii PGRP was confirmed by blastn analysis on NCBI and was designated as
Summary
The innate immune system is the first line of defense against invading microorganisms in vertebrates and the only line of defense in invertebrates and plants (Medzhitov and Janeway, 2002; Hoffmann, 2003). This system recognizes microorganisms through a series of pattern recognition receptors (PRRs) that have been highly conserved throughout evolution (Hoffmann et al, 1999; Janeway and Medzhitov, 2002). Short PGRPs are small extracellular proteins (19-20 kDa) that usually contain a signal peptide sequence and a PGRP domain. Long PGRPs often have multiple splice forms, such as BgPGRP-LA from Biomphalaria glabrata that has three isoforms (-LA, LA1 and -LA2) (Zhang et al, 2007)
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