Molecular characterization of an LRR-only protein gene in Pacific white shrimp Litopenaeus vannamei: Sequence feature, expression pattern, and protein activity

Expression characteristics and inhibitory activity of a leucine-rich repeat (LRR)-only protein in the Chinese mitten crab, Eriocheir sinensis

The leucine-rich repeat (LRR) domain is a crucial structure in a variety of immune related proteins and displays multiple immune functions. In this study, the open reading frame (ORF) of an LRR-only protein was cloned from the Chinese mitten crab, Eriocheir sinensis (EsLRRop1). The protein sequence of EsLRRop1 contained seven LRR motifs, three LRR-TYP motifs and an LRRCT motif. Tissue distribution exhibited that EsLRRop1 mainly expressed in nervous tissues including thoracic ganglion, eyestalk and brain while showed relatively lower transcriptional level in hemocyte. Based on the above expression characteristics, the responses of EsLRRop1 to the challenge of Vibrio parahaemolyticus and Staphylococcus aureus were tested. The result showed that the transcript of EsLRRop1 in thoracic ganglion and eyestalk up-regulated after being challenged with S. aureus, while it decreased post injection with V. parahaemolyticus. The transcript of EsLRRop1 in hemocytes up-regulated sharply at 3 h and decreased at 12 h and 24 h after being challenged with V. parahaemolyticus, while it decreased at 12 h and 24 h post injection with S. aureus. The recombinant protein of EsLRRop1 (His-EsLRRop1) displayed binding activities to V. alginolyticus, V. harveyi, V. parahaemolyticus, S. aureus, Corynebacterium glutamicum and Micrococcus lysodeikticus as well as lipopolysaccharide (LPS) and peptidoglycan (PGN). Moreover, the His-EsLRRop1 exhibited inhibitory activity against V. parahaemolyticus and V. harveyi with minimum inhibitory concentration (MIC) of 3.57-7.14 μM and 7.14-14.28 μM, respectively. These results provide theoretical basis for the application of EsLRRop1 in inhibiting bacteria in aquaculture practice.

The antibacterial activity and antibacterial mechanism analyses of an LRR-IG protein in the Chinese mitten crab, Eriocheir sinensis

Leucine-rich repeat and immunoglobulin domain containing protein (LRR-IG) family is an important class of immune molecules in invertebrates. Herein, a novel LRR-IG, named as EsLRR-IG5, was identified from Eriocheir sinensis. It contained typical structures of LRR-IG including an N-terminal LRR region and three IG domains. EsLRR-IG5 was ubiquitously expressed in all the tested tissues, and its transcriptional levels increased after being challenged with Staphylococcus aureus and Vibrio parahaemolyticus. Recombinant proteins of LRR and IG domains from the EsLRR-IG5 (named as rEsLRR5 and rEsIG5) were successfully obtained. rEsLRR5 and rEsIG5 could bind to both gram-positive bacteria and gram-negative bacteria as well as lipopolysaccharide (LPS) and peptidoglycan (PGN). Moreover, rEsLRR5 and rEsIG5 exhibited antibacterial activities against V. parahaemolyticus and V. alginolyticus and displayed bacterial agglutination activities against S. aureus, Corynebacterium glutamicum, Micrococcus lysodeikticus, V. parahaemolyticus and V. alginolyticus. The scanning electron microscopy (SEM) observation revealed that the membrane integrity of V. parahaemolyticus and V. alginolyticus was destroyed by rEsLRR5 and rEsIG5, which may lead to the leakage of cell contents and death. This study provided clues for further studies on the immune defense mechanism mediated by LRR-IG in crustaceans and provided candidate antibacterial agents for prevention and control of diseases in aquaculture.

A novel c-type lysozyme from Litopenaeus vannamei exhibits potent antimicrobial activity

Lysozyme is relevant to the innate immune system as a vital protein for crustaceans. In the present study, we cloned and characterized a novel c-type lysozyme gene (LvLYZ) from the Pacific white shrimp (Litopenaeus vannamei). The obtained full-length cDNA of LvLYZ was 990 bp and contained an open reading frame of 693 bp. Its deduced amino acid sequence consisted of 230 amino acids (aa) with a 17 aa signal peptide at the N-terminal and 130 aa functional domains. The multiple sequence alignment (MSA) indicated that the typical active sites in LvLYZ were similarly conserved as c-type lysozymes from other species. The transcription of LvLYZ appeared in all detected tissues and had relatively higher expression levels in hemocytes, hepatopancreas, gill and intestine. The mRNA expression profiles of LvLYZ were up-regulated in hemocyte and hepatopancreas post the stimulation of Vibrio parahaemolyticus or white spot syndrome virus (WSSV), respectively. The recombinant protein of LvLYZ (rLvLYZ) exhibited antibacterial activities against various microbes, including Escherichia coli, Vibrio splendidus, Micrococcaus luteus, Vibrio parahaemolyticus and Staphylococcus aureus. These results indicated that LvLYZ could cope with bacteria in L. vannamei and may play a significant role in immune response against invading pathogens.

A preliminary report of exploration of the exosomal shuttle protein in marine invertebrate Chlamys farreri

Exosomes are extracellular vesicles secreted by diverse cell under normal or abnormal physiological conditions, which could carry a range of bioactive molecules and play significant roles in biological processes, such as intercellular communication and immune response. In the current study, a preliminary study was performed to investigate the exosomal shuttle protein in Chlamys farreri (designated as CfesPro) and to predict the potential function of exosomes in scallop innate immunity. The serum derived exosomes (designated as CfEVs) were obtained from lipopolysaccharide (LPS)-stimulated C. farreri and untreated ones. After confirmation and characterization by transmission electron microscopy (TEM), nano-HPLC-MS/MS spectrometry was performed on CfEVs using a label-free quantitative method. Totally 2481 exosomal shuttle proteins were identified in CfEVs proteomic data, which included many innate immune related proteins. GO and KOG functional annotation showed that CfesPro participated in cellular processes, metabolism reactions, signaling transductions, immune responses and so on. Moreover, 1421 proteins in CfesPro were enriched to 324 pathways by KEGG analysis, including several immune-related pathways, such as autophagy, apoptosis and lysosome pathway. Meanwhile, eight autophagy-related proteins were initially identified in CfesPro, indicating that CfEVs had a potential role with autophagy. All these findings showed that CfEVs were involved in C. farreri innate immune defenses. This research would enrich the protein database of marine exosomes and provide a basis for the exploration of immune defense systems in marine invertebrates.