title: SmC2P1, a C2 domain protein from Scophthalmus maximus that binds bacterial pathogen-infected lymphocytes and reduces bacterial survival.
abstract: C2 domains are protein structural modules found in many eukaryotic proteins involved in signal transduction, membrane trafficking, and immune defense. Most of the studied C2 domain-containing proteins are multi-domained in structure, in which the C2 domain is an independently folded motif and plays an essential role in calcium-dependent membrane-targeting. Although C2 domains isolated from intact proteins have been studied for biological functions, no study on natural proteins containing C2 domain only has been documented. In this study, we identified a Scophthalmus maximus protein SmC2P1 that is comprised of a single C2 domain and lacks any other apparent domain structures. The deduced amino acid sequence of SmC2P1 contains 129 residues and shares 36-38% identities with the C2 domains of the perforins of several fish species. Like typical C2 domains, SmC2P1 is predicted to organize into eight beta-strands with a Ca(2+)-binding site located in inter-strand loops. SmC2P1 expression was detected, in deceasing order, in liver, spleen, blood, brain, muscle, kidney, gill, and heart. Experimental challenge of turbot with a bacterial pathogen significantly upregulated SmC2P1 expression in kidney in a time-dependent manner. Recombinant SmC2P1 purified from yeast exhibits no hemolytic activity but binds to pathogen-infected kidney lymphocytes in the presence of calcium. Furthermore, interaction of recombinant SmC2P1 with bacterium-infected lymphocytes reduced bacterial survival. These results indicate that SmC2P1 is a functional protein that is involved in host immune defense against bacterial infection.
authors.affiliation: Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, PR China.
authors.forename: Lu
authors.initials: L
authors.lastname: Zhao
authors.forename: Yong-hua
authors.initials: YH
authors.lastname: Hu
authors.forename: Li
authors.initials: L
authors.lastname: Sun
authors.forename: Jin-sheng
authors.initials: JS
authors.lastname: Sun
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D019295:Computational Biology; D017931:DNA Primers / Q000235:genetics; D020609:Edwardsiella tarda / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D004756:Enterobacteriaceae Infections / Q000276:immunology / Q000662:veterinary*; D005393:Fish Diseases / Q000235:genetics / Q000276:immunology*; D005412:Flatfishes; D007668:Kidney / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism* / Q000382:microbiology; D008969:Molecular Sequence Data; D054353:Perforin / Q000235:genetics / Q000276:immunology; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics*; D011506:Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017385:Sequence Homology
chemical_list: D017931:DNA Primers; D011506:Proteins; D054353:Perforin