title: Crystal structures for short-chain pentraxin from zebrafish demonstrate a cyclic trimer with new recognition and effector faces.
abstract: Short-chain pentraxins (PTXs), including CRP and SAP, are innate pattern recognition receptors that play vital roles in the recognition and elimination of various pathogenic bacteria by triggering the classical complement pathway through C1q. Similar to antibodies, pentraxins can also activate opsonisation and phagocytosis by interacting with Fc receptors (FcRs). Various structural studies on human PTXs have been performed, but there are no reports about the crystal structure of bony fish pentraxins. Here, the crystal structures of zebrafish PTX (Dare-PTX-Ca and Dare-PTX) are presented. Both Dare-PTX-Ca and Dare-PTX are cyclic trimers, which are new forms of crystallised pentraxins. The structures reveal that the ligand-binding pocket (LBP) in the recognition face of Dare-PTX is deep and narrow. Homology modelling shows that LBPs from different Dare-PTX loci differ in shape, reflecting their specific recognition abilities. Furthermore, in comparison with the structure of hCPR, a new C1q binding mode was identified in Dare-PTX. In addition, the FcR-binding sites of hSAP are partially conserved in Dare-PTX. These results will shed light on the understanding of a primitive PTX in bony fish, which evolved approximately 450 million years ago.
authors.affiliation: Department of Microbiology and Immunology, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing 100094, People's Republic of China.
authors.forename: Rong
authors.initials: R
authors.lastname: Chen
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology Immunology (CASPMI), Institute of Microbiology, Chinese Academy of Sciences (CAS), Chaoyang District, Beijing 100101, People's Republic of China.
authors.forename: Jianxun
authors.initials: J
authors.lastname: Qi
authors.affiliation: Department of Microbiology and Immunology, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing 100094, People's Republic of China.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Department of Microbiology and Immunology, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing 100094, People's Republic of China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.affiliation: Department of Microbiology and Immunology, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing 100094, People's Republic of China; Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing 100094, People's Republic of China. Electronic address: xiachun@cau.edu.cn.
authors.forename: Chun
authors.initials: C
authors.lastname: Xia
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D015922:Complement C1q / Q000378:metabolism; D017124:Conserved Sequence; D008958:Models, Molecular; D055503:Protein Multimerization; D011961:Receptors, Fc / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D029961:Zebrafish Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D011961:Receptors, Fc; D029961:Zebrafish Proteins; D015922:Complement C1q
keywords: Evolution; Pentraxin; Structure; Trimer; Zebrafish