Molecular cloning, characterization and expression analysis of trypsin-like serine protease from triangle-shell pearl mussel (Hyriopsis cumingii)

Cloning and functional analysis of a trypsin-like serine protease from Pinctada fucata martensii

Trypsin-like serine proteases (TLSs) play various roles in dietary protein digestion, hemolymph coagulation, antimicrobial peptide synthesis, and, in particular, the rapid immune pathways activated in response to pathogen detection. The cultured pearl industry, of which Pinctada fucata martensii is one of the most important species, is plagued by disease, thus leading to large economic losses. Herein, the molecular mechanisms underlying the innate immune response of P.f. martensii were explored. First, immune effector molecules from the P.f. martensii genome were screened and a TLS-like gene encoding a protein with a trypsin domain, herein designated as PmTLS, was identified. A multi-sequence alignment indicated a low sequence homology between PmTLS and other mollusk TLS-like proteins. Furthermore, a neighbor-joining phylogenetic analysis indicated that PmTLS has the closest genetic relationship to a Crassostrea gigas TLS. Additionally, real-time quantitative PCR (qPCR) analysis showed that PmTLS mRNA is constitutively expressed in all of the 6 examined P.f. martensii tissues, with significantly higher expression noted in hemocytes relative to the other tissues examined (p < 0.05). P.f. martensii samples were then challenged with various pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide, peptidoglycan, and polyinosinic acid. In the challenge groups, PmTLS was significantly upregulated in hemocytes at 48 h post-challenge when compared to the unchallenged controls. Furthermore, treatment with recombinant PmTLS (rPmTLS) also significantly inhibited the growth of most of the examined gram-negative bacteria tested in vitro (p < 0.05), but it had little effect on the growth of the examined gram-positive bacteria. When examining morphological changes via transmission electron microscopy, rPmTLS treated bacteria exhibited morphological changes such as plasma wall separation. Thus, rPmTLS appears to play a bactericidal role by destroying bacterial cell membranes or cell walls, which subsequently leads to a release of the cellular contents and cell death. The findings presented herein have enabled further characterization of the immune defense mechanisms in P.f. martensii and may lead to improved disease control methods for the pearl cultivation industry.

The C-terminal sequences of porcine thrombin are active as antimicrobial peptides

The C-terminal sequences of porcine thrombin encode a series of peptides with the characteristics of net positive charge and hydrophobicity, suggesting antimicrobial potential. In this study, we synthesized truncated C-terminal peptides to explore their antimicrobial potency and structure-activity relationship. The results showed that some peptides exerted antimicrobial activity against Gram-positive and Gram-negative bacteria, with selectivity for microbial membranes. The antimicrobial potency of the peptides increased with the extension of chain length. Considering toxicity to red blood cells, the 21-mer peptide T-6 displayed the highest therapeutic index of 43.4, suggesting its higher cell selectivity. Typical α-helical conformations were observed upon binding to a bacteria-mimicking environment. The derivatives tended to interact preferentially with negatively charged vesicles compared to zwitterionic vesicles. Flow cytometry and electron microscopy revealed that the peptides targeted bacterial cell membranes and disrupted cytoplasmic membrane integrity, thereby causing the release of cellular contents leading to cell death. Peptide-membrane interaction experiments provided evidence that the peptides killed bacteria via a membrane-mediating mechanism. In summary, the C-terminal sequence of porcine thrombin has antimicrobial functions.

Cloning and analysis of gene expression of interleukin-17 homolog in triangle-shell pearl mussel, Hyriopsis cumingii, during pearl sac formation

Successful allograft of mantle tissues in certain bivalve mollusks can form pearl sacs secreting nacre for pearl production. Little was known, however, about the immune consequences in response to the tissue transplantation. In the present study, interleukin (IL)-17, one of the key regulatory genes of alloimmunity, was cloned from the triangle-shell pearl mussel (HcIL-17) Hyriopsis cumingii by high-throughput sequencing of the mantle transcriptome. The sequence of HcIL-17 contains an open reading frame of 567 bp encoding a putative protein of 188 amino acid residues. Analysis of sequence characteristics, multiple sequence alignment and phylogenetic analysis indicated HcIL-17 was a novel member in the mollusk IL-17 family. Expression of the HcIL-17 gene in donor mantle tissues and in hemocytes of recipient mussel was up-regulated dramatically within 7 days in response to the mantle tissue allograft for pearl aquaculture, suggesting remarkable proinflammatory responses during pearl sac formation in triangle-shell pearl mussels. Analysis of the time-course expression of HcIL-17 gene revealed the induction of HcIL-17 was time-dependent, reflecting the different periods of alloimmune events in triangle-shell mussels. The results of this study provide essential background information for further investigation of mollusk alloimmunity.

Knockdown of Litopenaeus vannamei HtrA2, an up-regulated gene in response to WSSV infection, leading to delayed shrimp mortality

HtrA2 is an apoptosis-activating gene that enhances the apoptotic process by preventing the formation of the IAP-caspase complex, thereby freeing caspase to trigger the apoptosis pathway. In this study, we presented the full-length cDNA sequence of HtrA2 from Litopenaeus vannamei (LvHtrA2). The full-length LvHtrA2 was 1335 bp, encoding 444 amino acids. This deduced amino acid sequence contained five conserved domains: a mitochondrial targeting signal (MTS), a transmembrane (TM) domain, an IAP-binding motif (IBM), a trimerization motif, a serine protease domain, and a PDZ domain normally found in the HtrA2 proteins of other organisms. A phylogenetic analysis revealed that LvHtrA2 clustered with the HtrA2 from other invertebrates and was closely related to Penaeus monodon HtrA2 (PmHtrA2). RT-PCR with RNA extracts from L. vannamei revealed that LvHtrA2 expression was found in several tissues, including the lymphoid organs, the haemocytes, the hepatopancreas, the gill, and the stomach, with different expression levels. When determining the role of LvHtrA2 in WSSV infection, it was found that LvHtrA2 transcription was early up-regulated in the WSSV-infected shrimp at 8h post-infection (p.i.) and expression still remained high at 48 h p.i.. It also demonstrated that dsRNA specific to LvHtrA2 reduced the cumulative mortality in the WSSV-infected shrimp compared with the control group. Additionally, depletion of the LvHtrA2 transcripts reduced expression levels for caspase-3 (Cap-3) gene in shrimp. This result could suggest that LvHtrA2 may involved in apoptosis mediated mortality rather than providing immune protection during WSSV infection.