Identification of a novel C1q complement component in razor clam Sinonovacula constricta and its role in antibacterial activity

Invertebrate C1q Domain-Containing Proteins: Molecular Structure, Functional Properties and Biomedical Potential

C1q domain-containing proteins (C1qDC proteins) unexpectedly turned out to be widespread molecules among a variety of invertebrates, despite their lack of an integral complement system. Despite the wide distribution in the genomes of various invertebrates, data on the structure and properties of the isolated and characterized C1qDC proteins, which belong to the C1q/TNF superfamily, are sporadic, although they hold great practical potential for the creation of new biotechnologies. This review not only summarizes the current data on the properties of already-isolated or bioengineered C1qDC proteins but also projects further strategies for their study and biomedical application. It has been shown that further broad study of the carbohydrate specificity of the proteins can provide great opportunities, since for many of them only interactions with pathogen-associated molecular patterns (PAMPs) was evaluated and their antimicrobial, antiviral, and fungicidal activities were studied. However, data on the properties of C1qDC proteins, which researchers originally discovered as lectins and therefore studied their fine carbohydrate specificity and antitumor activity, intriguingly show the great potential of this family of proteins for the creation of targeted drug delivery systems, vaccines, and clinical assays for the differential diagnosis of cancer. The ability of invertebrate C1qDC proteins to recognize patterns of aberrant glycosylation of human cell surfaces and interact with mammalian immunoglobulins indicates the great biomedical potential of these molecules.

Effects of ammonia-N stress on molecular mechanisms associated with immune behavior changes in the haemocytes of Litopenaeus vannamei

High concentration of ammonia-N will inhibit the immune defense of aquatic animals. The neuroendocrine-immune (NEI) regulatory mechanism under ammonia-N stress has been systematically studied, but the final response mechanism of ammonia-N affecting the immune system remains unclear. To investigate the relationship among immune factors of Litopenaeus vannamei (L. vannamei) exposed to 0, 2, 10 and 20 mg/L ammonia-N, the determination of complement components, C-type lectins, proPO system, signal transduction pathway and phagocytosis as well as exocytosis were performed. The results showed that the expressions of complement components including C1q, MBL, ficolin and alpha-2 macroglobulin (A2M) and the complement receptor integrin were decreased significantly in ammonia-N treatment groups at 6,12 and 24 h. C-type lectins and signal transduction factors changed significantly. The decrease of phagocytosis-related genes and phagocytic activity were similar to the changes of complement components, C-type lectins and the signal pathway. The mRNA abundance of exocytosis-related genes was significantly down-regulated under ammonia-N exposure. Correspondingly, significantly changes occurred in the expressions of PPAE and PPO3, immune factors-related genes (Pen3, crustin, stylicins, ALFs and LYC) and inflammatory factors (HSP90, TNFα, IL-16) in haemocytes. Eventually, the serine proteinase activity, PO activity, antibacterial activity and bacteriolytic activity in plasma were decreased significantly. In addition, we speculated that under ammonia-N stress, phagocytosis and exocytosis were affected by complement components, and C-type lectins through intracellular signal transduction pathway. Complement components may involve in the regulation of proPO-activating system to response to ammonia-N stress. This study helped to further understanding the relationship among immune factors of crustacean in response to environmental stress, which implied that when it comes to the decrease of immunity affected by environmental stress, we should not only focus on the mechanism of upstream neuroendocrine response, but also pay attention to the role of immune factors.

Two fibrinogen-related proteins (FREPs) in the razor clam (Sinonovacula constricta) with a broad recognition spectrum and bacteria agglutination activity

Fibrinogen-related proteins (FREPs) that contain only the fibrinogen-related domain are likely involved in pathogen recognition. In this study, we identified two FREPs from the razor clam (Sinonovacula constricta), called ScFREP-1 and ScFREP-2, and investigated their roles in the immune response. Both ScFREP-1 and ScFREP-2 contained a fibrinogen-related domain at the C-terminal. ScFREP-1 and ScFREP-2 mRNAs were detected in all adult clam tissues tested, with the highest expression levels in the gill and mantle, respectively. Their expression levels were significantly upregulated after microbe infection. Recombinant ScFREPs could bind Gram-positive and Gram-negative bacteria as well as some pathogen-associated molecular patterns (PAMPs), and they could agglutinate those bacteria. These results showed that ScFREPs functioned as potential pattern recognition receptors to mediate immune response by recognizing PAMPs and agglutinating invasive microbes.

A sialic acid-binding lectin with bactericidal and opsonic activities from Ruditapes philippinarum

In the present study, a sialic acid-binding lectin was cloned and characterized from Manila clam Ruditapes philippinarum (designed as RpSabl). The open reading frame of RpSabl encoded a polypeptide of 162 amino acids with a calculated molecular mass of 17.7 kDa. Analysis of the conserved domain suggested that RpSabl was a new member of the sialic acid-binding lectins family. In non-stimulated clams, RpSabl transcripts were constitutively expressed in all five tested tissues, especially in hepatopancreas. After Vibrio anguillarum challenge, the expression of RpSabl mRNA in hepatopancreas was significantly up-regulated at 3 h (3.8-fold, P < 0.05), 6 h (4.9-fold, P < 0.05), 12 h (12.3-fold, P < 0.01) and 24 h (9.7-fold, P < 0.01), while RpSabl transcripts in hemocytes was only significantly up-regulated at 6 h (8.5-Fold, P < 0.01). RNAi-mediated knockdown of RpSabl transcripts affected the survival rates of Manila clam against V. anguillarum, perhaps mainly due to the inhibited expression of antibacterial effectors (e.g. lysozyme and defensin). Moreover, recombinant protein of RpSabl (rRpSabl) possessed binding activities towards lipopolysaccharides (LPS), peptidoglycan (PGN) and glucan in vitro. Coinciding with the Pathogen-associated molecular patterns (PAMPs) binding assay, rRpSabl displayed broad bacterial-agglutination properties towards Vibrio harveyi, Vibrio splendidus, V. anguillarum, Enterobacter cloacae and Aeromonas hydrophila. Meanwhile, the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rRpSabl incubation. All these results showed that RpSabl could function as a versatile molecule involved in the innate immune responses of R. philippinarum.