Identification and characterization of a novel interaction between pulmonary surfactant protein D and decorin.
Surfactant-associated protein D (SP-D) is a collectin that is present in lung surfactant and mucosal surfaces. Although SP-D regulates diverse functions, only a few proteins are known to bind to this collectin. Here we describe the co-purification of decorin, a novel SP-D-binding protein, from amniotic fluid. The human decorin that co-purified with SP-D is a 130-150-kDa proteoglycan, which has a 46-kDa protein core and approximately 90-kDa dermatan sulfate chain. Both native and recombinant decorin can bind to SP-D that is already bound to maltose-agarose matrix, and these SP-D-decorin complexes are dissociated at high salt (0.5-1.0 m NaCl) conditions, releasing the decorin. We further show that SP-D and decorin interact with each other (kd = 4 nm) by two mechanisms. First, the direct binding and competition experiments show that the carbohydrate recognition domain (CRD) of SP-D binds in a calcium dependent-manner to the sulfated N-acetyl galactosamine moiety of the glycosaminoglycan chain. Second, complement component C1q, a complement protein that is known to interact with decorin core protein via its collagen-like region, partially blocks the interaction between decorin and native SP-D. This protein, however, does not block the interaction between decorin and SP-D(n/CRD), a recombinant fragment that lacks the N-terminal and collagen-like regions. Furthermore, the core protein, obtained by chondroitin ABC lyase treatment of decorin, binds SP-D, but not SP-D(n/CRD). These findings suggest that decorin core protein binds the collagen-like region of the SP-D. Concentrations of decorin and SP-D are negatively correlated to each other, in amniotic fluid, implying a functional relevance for SP-D-decorin interaction, in vivo. Collectively, our results show that carbohydrate recognition domains of SP-D interact with the dermatan sulfate moiety of decorin via lectin activity and that the core protein of decorin binds the collagen-like region of SP-D in vitro, and these interactions may be operative in vivo.
Medical Research Council Immunochemistry Unit, Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, United Kingdom.
Jeya
J
Nadesalingam
Andres Lopez
AL
Bernal
Alister W
AW
Dodds
Antony C
AC
Willis
David J
DJ
Mahoney
Anthony J
AJ
Day
Kenneth B M
KB
Reid
Nades
N
Palaniyar
D000116:Acetylgalactosamine / Q000378:metabolism; D000653:Amniotic Fluid / Q000378:metabolism; D001667:Binding, Competitive; D019921:Biotinylation; D002122:Calcium Chloride / Q000494:pharmacology; D002241:Carbohydrates / Q000737:chemistry; D002850:Chromatography, Gel; D015922:Complement C1q / Q000378:metabolism; D058575:Decorin; D003871:Dermatan Sulfate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D016326:Extracellular Matrix Proteins; D006025:Glycosaminoglycans / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008320:Maltose / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry; D012685:Sepharose / Q000494:pharmacology; D020349:Surface Plasmon Resonance; D013997:Time Factors
D002241:Carbohydrates; C546878:DCN protein, human; D058575:Decorin; D016326:Extracellular Matrix Proteins; D006025:Glycosaminoglycans; D008024:Ligands; D011509:Proteoglycans; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D011994:Recombinant Proteins; D003871:Dermatan Sulfate; D008320:Maltose; D015922:Complement C1q; D012685:Sepharose; D000116:Acetylgalactosamine; D002122:Calcium Chloride