title: A novel multi-domain C1qDC protein from Zhikong scallop Chlamys farreri provides new insights into the function of invertebrate C1qDC proteins.
abstract: The C1q domain containing (C1qDC) proteins are a family of proteins possessing globular C1q (gC1q) domains, and they rely on this domain to recognize various ligands such as PAMPs, immunoglobulins, ligands on apoptotic cell. In the present study, a novel multi-domain C1qDC protein (CfC1qDC-2) was identified from scallop Chlamys farreri, and its full length cDNA was composed of 1648 bp, encoding a signal peptide and three typical gC1q domains. BLAST analysis revealed significant sequence similarity between CfC1qDC-2 and C1qDC proteins from mollusks. Three gC1q domains were predicted in its tertiary structure to form a tightly packed bell-shaped trimer, and each one adopted a typical 10-stranded sandwich fold with a jelly-roll topology and contained six aromatic amino acids forming the hydrophobic core. The mRNA transcripts of CfC1qDC-2 were mainly detected in the tissues of hepatopancreas and gonad of adult scallops, and the expression level was up-regulated in hemocytes after stimulated by LPS, PGN and β-glucan. During the embryonic development of scallop, the mRNA transcripts of CfC1qDC-2 were presented in all the detected stages, and the expression level was up-regulated from D-hinged larvae and reached the highest at eye-spot larvae. The recombinant protein of MBP-CfC1qDC-2 (rCfC1qDC-2) could bind various PAMPs including LPS, PGN, LTA, β-glucan, mannan as well as polyI:C, and different microorganisms including three Gram-negative bacteria, three Gram-positive bacteria and two yeasts, as well as scallop apoptotic cells. Meanwhile, rCfC1qDC-2 could interact with human heat-aggregated IgG and IgM, and inhibit the C1q-dependent hemolysis of rabbit serum. All these results indicated that CfC1qDC-2 could recognize not only PAMPs as a PRR, but also the apoptotic cells. Moreover, the similar structures and functions shared by CfC1qDC-2 and complement C1q provided a new insight into the evolution of C1qDC proteins in complement system.
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China; Lianyungang Maternal and child Health Hospital, Lianyungang 222001, China.
authors.forename: Leilei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China. Electronic address: wanglingling@ms.qdio.ac.cn.
authors.forename: Lingling
authors.initials: L
authors.lastname: Wang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Daoxiang
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Qiufen
authors.initials: Q
authors.lastname: Jiang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Sun
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China.
authors.forename: Huan
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Dalian Ocean University, Dalian 116023, China.
authors.forename: Linsheng
authors.initials: L
authors.lastname: Song
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D015922:Complement C1q / Q000737:chemistry / Q000502:physiology*; D017124:Conserved Sequence; D015870:Gene Expression; D006434:Hemocytes / Q000276:immunology / Q000378:metabolism; D006461:Hemolysis; D006801:Humans; D007113:Immunity, Innate; D007074:Immunoglobulin G / Q000737:chemistry; D007075:Immunoglobulin M / Q000737:chemistry; D008070:Lipopolysaccharides / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009928:Organ Specificity; D000069452:Pathogen-Associated Molecular Pattern Molecules / Q000378:metabolism; D049897:Pectinidae / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D014733:Vibrio / Q000276:immunology
chemical_list: D007074:Immunoglobulin G; D007075:Immunoglobulin M; D008070:Lipopolysaccharides; D000069452:Pathogen-Associated Molecular Pattern Molecules; D015922:Complement C1q
keywords: Apoptotic cell binding; C1qDC proteins; Immune recognition; Immunoglobulin binding