MOLECULAR AND TRANSCRIPTIONAL CHARACTERIZATION OF TWO C1Q/TNF-RELATED PROTEINS (CTRPS) FROM RED-LIP MULLET Liza haematocheilus

C1q is a pattern recognition protein mainly involve in complement pathway. It is the key crosslinker between innate immunity and adaptive immunity. C1q has a hexadimeric structure which contain N terminal collagen-like region and C-terminal globular C1q (gC1q) domain. The gC1q is a ligand recognition domain which induce the conformational changes in collagen region while binding C1q to IgG or IgM containing immune complexes. These phenomena eventually lead to activation of complement pathway. The gC1q is also can be found in various non-complement proteins and it has structural and evolutionary relationship with tumor necrosis factor (TNF) thus form the C1q and TNF superfamily comprise with verity of proteins. In this study, CTRP4-like and 6 from red-lip mullet were investigated for molecular and transcriptional characteristics to get better understanding about their expression patterns in normal conditions and against bacterial and PAMP stimuli which might be helpful to explore functional behaviors of these proteins. ORF of ChCTRP4-like coding a protein sequence with 375 amino acids with 41.86 kDa molecular weight and theoretical isoelectric point (pI) is 9.33. The theoretical pI, molecular mass and amino acids of encoded protein sequence by ORF of ChCTRP6 are 8.55, 27.17 kDa and 242 amino acids respectively. ChCTRP4-like shares highest identity (80.3%) and similarity (86.4%) with Acanthochromis polyacanthus while having lowest identity (42.9%) and similarity (56.1%) with Mus musculus. ChCTRP6 shares highest identity (88.0%) and similarity (93.4%) with Labrus bergylta while having lowest identity (47.8%) and similarity (63.6%) with Homo sapiens. According to the multiple sequence alignment ChCTRP4-like contain two C1q domains between 57-184 and 222-362 amino acid residues. Further, it does not contain signal peptide and N- linked glycosylation site can be found at ²⁶³NKSS²⁶⁶. ChCTRP6 only one C1q domain between 110-237 amino acids and it has cleavage site between 17-18 amino acids but no N-linked glycosylation site. According to the tissue specific mRNA distribution, both ChCTRPs highly express in blood. According to the immune challenge in blood, ChCTRP4-like and ChCTRP6 show significant transcript expression against all the stimuli; LPS, Poly:IC and L. gaevieae . Highest expression of ChCTRP4-like can be observed against L. gaevieae and highest expression of ChCTRP6 can be observed against poly:IC. According to the results obtained, both ChCTRP4-like and ChCTRP6 show immune responses towards bacterial and PAMP stimuli. These ChCTRPs are reported to contain hormonal function and some structural functions. CTRP4-like was identified but not characterized, and, hence, its physiological function remains unknown. ChCTRP6 is reported to involve in inhibiting alternative complement pathway activation. Based on results revealed from the study, we can conclude that both ChCTRP4-like and ChCTRP6 are immunologically important genes.