Abstract
C1q-domain-containing (C1qDC) proteins are a family of proteins with a globular C1q (gC1q) domain and participate in several immune responses. In this study, a C1qDC gene was identified from the triangle-shell pearl mussel Hyriopsis cumingii (designated as HcC1qDC6). This gene has a full-length cDNA of 1782 bp and an open reading frame of 1,335 bp that encodes a 444-amino acid polypeptide containing three gC1q domains. HcC1qDC6 contains at least five exons and four introns. The mRNA transcripts of HcC1qDC6 were found to have the highest expression levels in the mantle tissue. The expression levels in the mantle and hepatopancreas were significantly upregulated by Staphylococcus aureus and Vibrio parahaemolyticus challenges. Moreover, knockdown of HcC1qDC6 inhibits the expression of two immune-related genes (tumor necrosis factor and whey acidic protein). The recombinant proteins of C1q1, C1q2, and C1q3 all exhibit a binding activity against seven bacterial species and directly bind to peptidoglycan and lipopolysaccharide. The results indicate that HcC1qDC6 is involved in the innate immunity of H. cumingii.
Highlights
C1q is a subcomponent of the classical pathway of the complement system and a major connecting link between the innate and antibody-mediated acquired immunity (Gaboriaud et al, 2003; Kishore et al, 2004; Ghebrehiwet et al, 2012)
CgC1qDC-1 from C. gigas has high binding specificity and affinity to lipopolysaccharides (LPS). This protein serves as a pattern recognition receptor (PRR) and opsonin involved in the immune response against invading Gram-negative bacteria (Jiang et al, 2015)
C1qDC proteins can recognize a remarkable variety of non-self ligands, including certain bacteria, viruses, parasites, and mycoplasmas, through the globular C1q (gC1q) domain (Kishore et al, 2004; Ghebrehiwet et al, 2012)
Summary
C1q is a subcomponent of the classical pathway of the complement system and a major connecting link between the innate and antibody-mediated acquired immunity (Gaboriaud et al, 2003; Kishore et al, 2004; Ghebrehiwet et al, 2012). HcC1qDC6 Involved in Innate Immune of Hyriopsis cumingii head C1q (ghC1q) proteins only have a short N-terminal amino acid sequence with signal peptide, coiled coil, and other sequence motifs (Carland and Gerwick, 2010). Two novel gC1q-domain-containing proteins, namely, AiC1qDC-1 and AiC1qDC-2, from bay scallop Argopecten irradians agglutinate various microorganisms and bind different pathogen-associated molecular patterns (PAMPs; Kong et al, 2010; Wang et al, 2012a). CgC1qDC-1 from C. gigas has high binding specificity and affinity to lipopolysaccharides (LPS) This protein serves as a pattern recognition receptor (PRR) and opsonin involved in the immune response against invading Gram-negative bacteria (Jiang et al, 2015). The HcC1qDC6 transcript is upregulated under bacterial stimulation and its protein binds to different microorganisms and carbohydrates, preventing bacterial infections
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