The novel avian protein, AWAK, contains multiple domains with homology to protease inhibitory modules

Role of Marsupenaeus japonicus crustin-like peptide against Vibrio penaeicida and white spot syndrome virus infection

Crustins are important AMP that has been identified in crustaceans. In this study, the role of Marsupenaeus japonicus crustin-like peptide (MjCRS) was examined in vivo by RNA interference (RNAi) using double-stranded RNA (dsRNA). Tissue expression analysis revealed that MjCRS transcripts are expressed in different tissues tested with the highest expression observed in hemocytes. Treatment with double-stranded RNA specific to MjCRS led to a significant reduction of MjCRS transcripts within the hemocytes. When MjCRS was silenced and subsequently infected with Vibrio penaeicida final mortality was significantly higher compared with PBS and dsGFP treated groups. On the other hand, final mortalities of MjCRS silenced and PBS injected groups were not significantly different after infection with white spot virus, however, both are significantly higher compared with dsGFP treated group. V. penaeicida infection significantly decreased MjCRS expression at 3, 6, 12 and 24h followed by significant increase at 48 h post-infection. On the contrary, white spot infection significantly increased MjCRS expression at 6 and 12h and decreased at 48 h post-infection. dsRNA treatment alone decreased total hemocyte counts (THCs) and subsequent V. penaeicida or white spot virus infection further decreased THCs. VP28 gene expression was both similarly increased in PBS injected group and MjCRS silenced group at 24 and 48 h-post infection. Results suggest that MjCRS is involved in antibacterial defense and might not have critical function against viral infection.

A double WAP domain-containing protein Es-DWD1 from Eriocheir sinensis exhibits antimicrobial and proteinase inhibitory activities

Whey acidic proteins (WAP) belong to a large gene family of antibacterial peptides, which are critical in the host immune response against microbial invasion. The common feature of these proteins is a single WAP domain maintained by at least one four-disulfide core (4-DSC) structure rich in cysteine residues. In this study, a double WAP domain (DWD)-containing protein, Es-DWD1, was first cloned from the Chinese mitten crab (Eriocheirsinensis). The full-length Es-DWD1cDNA was 1193 bp, including a 411 bp open reading frame (ORF) encoding 136 amino acids with a signal peptide of 22 amino acids in the N-terminus. A comparison with other reported invertebrate and vertebrate sequences revealed the presence of WAP domains characteristic of WAP superfamilies. As determined by quantitative real-time RT-PCR, Es-DWD1 transcripts were ubiquitously expressed in all tissues, but it was up-regulated in hemocytes post-challenge with pathogen-associated molecular patterns (PAMPs). The mature recombinant Es-DWD1 (rEs-DWD1) protein exhibited different binding activities to bacteria and fungus. Moreover, rEs-DWD1 could exert agglutination activities against Bacillus subtilis and Pichiapastoris and demonstrated inhibitory activities against the growth of Staphylococcus aureus, Aeromonas hydrophila and P. pastoris. Furthermore, rEs-DWD1 showed a specific protease inhibitory activity in B. subtilis. Coating of rEs-DWD1 onto agarose beads enhanced encapsulation of the beads by crab hemocytes. Collectively, the results suggest that Es-DWD1 is a double WAP domain containing protein with antimicrobial and proteinase inhibitory activities, which play significant roles in the immunity of crustaceans.

Mj-DWD, a double WAP domain-containing protein with antiviral relevance in Marsupenaeus japonicus

The Mj-DWD (Marsupenaeus japonicus' double-WAP domains) gene was originally found up-regulated in virus-resistant shrimp M. japonicus by suppression subtractive hybridization (SSH). The full-length cDNA of Mj-DWD encodes a novel protein containing a KGD (Lys-Gly-Asp) motif and double WAP domains. Performed by quantitative real-time PCR, the expression level of Mj-DWD gene was consistently maintained at a high level in the newly prepared virus-resistant shrimp compared to the normal one. In addition, the Mj-DWD gene was also found to be rapidly up-regulated by WSSV infection during the early phase. Furthermore, the recombinant Mj-DWD, expressed by Pichia pastoris, showed specific protease inhibitory activity on Bacillus subtilis. These findings suggest that Mj-DWD plays an important role in the host defence system against WSSV infection in M. japonicus, possibly through its protease inhibitory activity.

Functional domains of the human epididymal protease inhibitor, eppin

Eppin has two potential protease inhibitory domains: a whey acid protein or four disulfide core domain and a Kunitz domain. The protein is also reported to have antibacterial activity against Gram-negative bacteria. Eppin and its whey acid protein and Kunitz domains were expressed in Escherichia coli and their ability to inhibit proteases and kill bacteria compared. The Kunitz domain inhibits elastase (EC 3.4.21.37) to a similar extent as intact eppin, whereas the whey acid protein domain has no such activity. None of these fragments inhibits trypsin (EC 3.4.21.4) or chymotrypsin (EC 3.4.21.1) at the concentrations tested. In a colony forming unit assay, both domains have some antibacterial activity against E. coli, but this was not to the same degree as intact eppin or the two domains together. When bacterial respiratory electron transport was measured using a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide assay, eppin and its domains caused an increase in the rate of respiration. This suggests that the mechanism of cell killing may be partly through the permeablization of the bacterial inner membrane, resulting in uncoupling of respiratory electron transport and consequent collapse of the proton motive force. Thus, we conclude that although both of eppin's domains are involved in the protein's antibacterial activity, only the Kunitz domain is required for selective protease inhibition.

Crustins: enigmatic WAP domain-containing antibacterial proteins from crustaceans

Crustins are antibacterial proteins of ca. 7-14 kDa with a characteristic four-disulphide core-containing whey acidic protein (WAP) domain, expressed by the circulating haemocytes of crustaceans. Over 50 crustin sequences have been now reported from a variety of decapods, including crabs, lobsters, shrimp and crayfish. Three main types seem to occur but all possess a signal sequence at the amino terminus and a WAP domain at the carboxyl end. Differences between types lie in the structure of the central region. Those crustins purified as the native protein or expressed recombinantly all kill Gram-positive bacteria, and gene studies have shown that they are constitutively expressed, often at high levels, but show no consistent patterns of change in expression following injection of bacteria. This variable response to infection is enigmatic but indicates that these proteins could perform additional functions, perhaps as immune regulators in recovery from wounding, trauma or physiological stress.

Isolation and characterization of antimicrobial proteins and peptide from chicken liver

Endogenous antimicrobial peptides and proteins are crucial components of the innate immune system and play an essential role in the defense against infection. Antimicrobial activity was detected in the acid extract of livers harvested from healthy adult White Leghorn hens, Gallus gallus. Two antimicrobial proteins and one antimicrobial polypeptide were isolated from the liver extract by cation-exchange and gel filtration chromatography, followed by two-step reverse-phase high-performance liquid chromatography (RP-HPLC). These antimicrobial components were identified as histones H2A and H2B.V, and histone H2B C-terminal fragment using peptide mass fingerprinting and partial sequencing by tandem nanoelectrospray mass spectrometry. The proteins and the peptide identified in the present study, which exhibited antimicrobial activity against both Gram-positive and Gram-negative bacteria, were thermostable and showed salt-resistant activity. The antimicrobial properties of histones and histone fragment in chicken provide further evidence that histones, in addition to their role in nucleosome formation, may play an important role in innate host defense against intracellular or extracellular microbe invasion in a wide range of animal species.

Characterization of AWAP IV, the C-terminal domain of the avian protein AWAK

AWAP IV constitutes the C-terminal domain of the larger 81 kDa protein AWAK [Avian WAP (whey acidic protein) domain- and Kunitz domain-containing], which is predicted, through conserved domain database searching, to contain at least four WAP domains and one Kunitz domain. RT (reverse transcription)–PCR analyses revealed mRNA transcripts encoding AWAP IV in the small intestinal and kidney tissues of 5-day-old Salmonella-infected chicks. Time-kill antimicrobial assays using rAWAP IV (recombinant AWAP IV) cell lysate indicated antimicrobial activity against Gram-positive and Gram-negative bacteria including Salmonella, Streptococcus and Staphylococcus spp. In addition, permeabilization of the outer membrane of Salmonella, as shown by the NPN (N-phenyl-1-naphthylamine) fluorescent probe assay, supported the ability of rAWAP IV to disrupt prokaryotic membranes. WAP domains can function as inhibitors of serine protease activity, and the microbial serine proteases subtilisin and proteinase K were inhibited by rAWAP IV cell lysate. However, at comparable concentrations, no significant inhibition of the mammalian serine protease elastase was observed. The combined broad-spectrum antibacterial and anti-protease activities of AWAP IV suggest a novel role in the avian innate defence mechanisms operating against microbial infection.