title: Molecular characteristics of hemoglobins in blood clam and their immune responses to bacterial infection.
abstract: Bivalve hemoglobins have antibacterial activities, while the underlying mechanisms remain poorly understood. In our study, three full-length cDNAs of hemoglobins from blood clam skHbs were obtained, encoding putative polypeptides of 147, 150, and 152 amino acids, respectively. Predicted advanced protein structures showed that the skHbs had amphipathic antibacterial structures, displayed the typical structural characteristics of proteins with globin-like fold containing numerous alpha-helixes, and forming a homodimeric skHbI and a heterotetrameric skHbII complex. After injected with alive and heat-killed Gram-positive bacteria Bacillus subtilis, the mRNA levels of skHbI and skHbII were both significantly upregulated through increasing the expression of peptidoglycan recognition protein-like (PGRP-like) protein and Toll-like receptor (TLR-like) protein induced by peptidoglycan on the surface of the bacteria, but there were no obvious differences in their protein levels. Besides, reactive oxygen species (ROS) was detected to participate in the resistance to B. subtilis. These implied that skHbs could involve in the innate immune responses to Gram-positive bacterial infection directly with their amphipathic structures and indirectly by increasing ROS production through PGRP triggering Toll pathway. In conclusion, our findings reveal the structural characteristics of skHbs and their mechanism against Gram-positive bacteria thereby providing the molecular evidence for fundamental innate antibacterial activities by invoking respiratory proteins.
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Xu
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China; Department of Biology, Medical College, Qingdao University, Qingdao 266021, China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China; Department of Histology and Embryology, Medical College, Qingdao University, Qingdao 266021, China.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Jing
authors.affiliation: Department of Marine Biology, College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China. Electronic address: tjfan@ouc.edu.cn.
authors.forename: Tingjun
authors.initials: T
authors.lastname: Fan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001412:Bacillus subtilis / Q000502:physiology*; D001483:Base Sequence; D049872:Bivalvia / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D002352:Carrier Proteins / Q000378:metabolism; D003001:Cloning, Molecular; D006434:Hemocytes / Q000276:immunology / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007113:Immunity, Innate; D008958:Models, Molecular; D010802:Phylogeny; D011487:Protein Conformation; D017382:Reactive Oxygen Species / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D006454:Hemoglobins; D017382:Reactive Oxygen Species; D051193:Toll-Like Receptors; C118897:peptidoglycan recognition protein
keywords: Antibacterial activity; Gram-positive bacterial infection; Hemoglobin; Innate immune response; Structural characteristic; Toll pathway