Molecular and functional characterization of ApPGRP from Anatolica polita in the immune response to Escherichia coli

Identification and functional characterization of a long-type peptidoglycan recognition protein, PGRP-L in amphibian Xenopus laevis

Peptidoglycan recognition proteins (PGRPs) are a family of multifunctional proteins playing vital roles in PGN metabolism and antibacterial defense, and their functions have been well-characterized in mammals, bony fishes, and insects. However, the information about the functions of amphibian long-type PGRP is rather limited. Here, we identified and cloned a long-type PGRP gene (named Xl-PGRP-L) from African clawed frog, Xenopus laevis. Xl-PGRP-L gene was detected in all orangs/tissues examined, and was rapidly induced in intestine, liver, and lung following the stimulation of PGN. Sequence analysis showed that Xl-PGRP-L possesses four Zn2+-binding residues (His358, Tyr395, His470, and Cys478) required for amidase activity of catalytic PGRPs, and assays for amidase activity revealed that recombinant Xl-PGRP-L cloud degrade PGN in a Zn2+-dependent manner, indicating that Xl-PGRP-L is belonging to catalytic PGRPs. In addition, Xl-PGRP-L have antibacterial activity against Gram-negative bacteria Edwardsiella tarda and Gram-positive bacteria Streptococcus agalactiae. The present investigation represents the first characterization regarding the biological activities of amphibian long-type PGRPs, thus contributes to a better understanding of the functions of tetrapod PGRPs and the molecular mechanisms of amphibian antibacterial defense.

Short peptidoglycan recognition protein 5 modulates immune response to bacteria in Indian major carp, Cirrhinusmrigala

Peptidoglycan recognition proteins (PGRPs) function in host antibacterial responses by recognizing bacterial peptidoglycan (PGN). In the present study, a short pgrp5 (named mpgrp5) was identified in Cirrhinus mrigala (mrigal). The full-length cDNA of the mpgrp5 gene was 1255 bp, containing an open reading frame of 746 bp encoding a protein of 248 amino acids. The predicted protein contained the typical Pgrp/amidase domain, conserved Zn2+, and PGN binding residues. The phylogenetic analysis revealed that the mpgrp5 is closely related to Pgrps reported in Labeo rohita, Cyrinus carpio, and Ctenopharyngodon idella. The ontogenetic expression of mpgrp5 was highest at 7 days post-hatching (dph) and its possible maternal transfer. mpgrp5 was constitutively expressed in all tissues examined, with the highest expression observed in the intestine. Furthermore, mpgrp5 was found upregulated in mrigal post-challenge in a time-dependent manner at 6hpi in the liver (3.16 folds, p < 0.05) and kidney (2.79 folds, p < 0.05) and at 12hpi in gill (1.90 folds, p < 0.01), skin (1.93 folds, p < 0.01), and intestine, (2.71 folds, p < 0.05) whereas at 24hpi in spleen (4.0 folds, p < 0.01). Our results suggest that mpgrp5 may play an important role in antibacterial immune response from early life stages in mrigal.

Ribosomally synthesized peptides, foreground players in microbial interactions: recent developments and unanswered questions

It is currently well established that multicellular organisms live in tight association with complex communities of microorganisms including a large number of bacteria. These are immersed in complex interaction networks reflecting the relationships established between them and with host organisms; yet, little is known about the molecules and mechanisms involved in these mutual interactions. Ribosomally synthesized peptides, among which bacterial antimicrobial peptides called bacteriocins and microcins have been identified as contributing to host-microbe interplays, are either unmodified or post-translationally modified peptides. This review will unveil current knowledge on these ribosomal peptide-based natural products, their interplay with the host immune system, and their roles in microbial interactions and symbioses. It will include their major structural characteristics and post-translational modifications, the main rules of their maturation pathways, and the principal ecological functions they ensure (communication, signalization, competition), especially in symbiosis, taking select examples in various organisms. Finally, we address unanswered questions and provide a framework for deciphering big issues inspiring future directions in the field.

Tenebrio molitor PGRP-LE Plays a Critical Role in Gut Antimicrobial Peptide Production in Response to Escherichia coli

Invading pathogens are recognized by peptidoglycan recognition proteins (PGRPs) that induce translocation of NF-κB transcription proteins and expression of robust antimicrobial peptides (AMPs). Tenebrio molitor PGRP-LE (TmPGRP-LE) has been previously identified as a key sensor of Listeria monocytogenes infection. Here, we present that TmPGRP-LE is highly expressed in the gut of T. molitor larvae and 5-day-old adults in the absence of microbial infection. In response to Escherichia coli and Candida albicans infections, TmPGRP-LE mRNA levels are significantly upregulated in both the fat body and gut. Silencing of TmPGRP-LE by RNAi rendered T. molitor significantly more susceptible to challenge by E. coli infection and, to a lesser extent, Staphylococcus aureus and C. albicans infections. Reduction of TmPGRP-LE levels in the larval gut resulted in downregulation of eight AMP genes following exposure to E. coli, S. aureus, and C. albicans. However, the transcriptional levels of AMPs more rapidly reached a higher level in the dsEGFP-treated larval gut after challenge with E. coli, which may suggest that AMPs induction were more sensitive to E. coli than S. aureus and C. albicans. In addition, TmPGRP-LE RNAi following E. coli and C. albicans challenges had notable effects on TmRelish, TmDorsal X1 isoform (TmDorX1), and TmDorX2 expression level in the fat body and gut. Taken together, TmPGRP-LE acts as an important gut microbial sensor that induces AMPs via Imd activation in response to E. coli, whereas involvement of TmPGRP-LE in AMPs synthesize is barely perceptible in the hemocytes and fat body.