Nucleic acid is a novel ligand for innate, immune pattern recognition collectins surfactant proteins A and D and mannose-binding lectin.
Collectins are a family of innate immune proteins that contain fibrillar collagen-like regions and globular carbohydrate recognition domains (CRDs). The CRDs of these proteins recognize various microbial surface-specific carbohydrate patterns, particularly hexoses. We hypothesized that collectins, such as pulmonary surfactant proteins (SPs) SP-A and SP-D and serum protein mannose-binding lectin, could recognize nucleic acids, pentose-based anionic phosphate polymers. Here we show that collectins bind DNA from a variety of origins, including bacteria, mice, and synthetic oligonucleotides. Pentoses, such as arabinose, ribose, and deoxyribose, inhibit the interaction between SP-D and mannan, one of the well-studied hexose ligands for SP-D, and biologically relevant d-forms of the pentoses are better competitors than the l-forms. In addition, DNA and RNA polymer-related compounds, such as nucleotide diphosphates and triphosphates, also inhibit the carbohydrate binding ability of SP-D, or approximately 60 kDa trimeric recombinant fragments of SP-D that are composed of the alpha-helical coiled-coil neck region and three CRDs (SP-D(n/CRD)) or SP-D(n/CRD) with eight GXY repeats (SPD(GXY)(8)(n/CRD)). Direct binding and competition studies suggest that collectins bind nucleic acid via their CRDs as well as by their collagen-like regions, and that SP-D binds DNA more effectively than do SP-A and mannose-binding lectin at physiological salt conditions. Furthermore, the SP-D(GXY)(8)(n/CRD) fragments co-localize with DNA, and the protein competes the interaction between propidium iodide, a DNA-binding dye, and apoptotic cells. In conclusion, we show that collectins are a new class of proteins that bind free DNA and the DNA present on apoptotic cells by both their globular CRDs and collagen-like regions. Collectins may therefore play an important role in decreasing the inflammation caused by DNA in lungs and other tissues.
Palaniyar
Nades
N
MRC Immunochemistry Unit, Department of Biochemistry, The University of Oxford, Oxford OX1 3QU, United Kingdom. Nades@bioch.ox.ac.uk
Nadesalingam
Jeya
J
Clark
Howard
H
Shih
Michael J
MJ
Dodds
Alister W
AW
Reid
Kenneth B M
KB
D000818:Animals; D017209:Apoptosis; D001667:Binding, Competitive; D019921:Biotinylation; D015153:Blotting, Western; D002241:Carbohydrates / Q000737:chemistry; D002455:Cell Division; D003094:Collagen / Q000737:chemistry; D037222:Collectins / Q000737:chemistry*; D004396:Coloring Agents / Q000494:pharmacology; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007249:Inflammation; D019169:Jurkat Cells; D008024:Ligands; D008168:Lung / Q000378:metabolism; D037601:Mannose-Binding Lectin / Q000737:chemistry*; D051379:Mice; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009841:Oligonucleotides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011108:Polymers / Q000737:chemistry; D011419:Propidium / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D037662:Pulmonary Surfactant-Associated Protein A / Q000737:chemistry*; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry*; D012313:RNA / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D020349:Surface Plasmon Resonance; D013997:Time Factors
D002241:Carbohydrates; D037222:Collectins; D004396:Coloring Agents; D008024:Ligands; D037601:Mannose-Binding Lectin; D009841:Oligonucleotides; D011108:Polymers; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D011994:Recombinant Proteins; D011419:Propidium; D012313:RNA; D003094:Collagen; D004247:DNA