Limited proteolysis of surfactant protein D causes a loss of its calcium-dependent lectin functions.
Surfactant protein D (SP-D) is a multimeric collagenous lectin that mediates the clearance of pathogens and modulates immune cell functions via its C-terminal carbohydrate recognition domain (CRD). We hypothesized that extracellular proteolysis of SP-D may result in a loss of its functional properties. Multimeric SP-D was partially digested by human leukocyte elastase (HLE) dose- and time-dependently. Physiologic concentrations of calcium slowed, but did not protect from degradation. In solution, both native and degraded SP-D had an apparent molecular weight of 650 to >1000 kDa. Under reducing conditions, the degraded SP-D monomers run at 10 kDa less than native SP-D. Amino acid sequencing located all major cleavage sites into the CRD. Functional studies showed that degraded SP-D had lost its calcium-dependent lectin properties, i.e. neither bound to mannose nor agglutinated bacteria. These studies demonstrate that elastase results in the limited proteolysis of SP-D with loss of its CRD-dependent activities and suggest that proteases at concentrations observed in various lung diseases may impair the antimicrobial and immunomodulatory roles of SP-D.
Griese
M
M
The Lung Research Group, Children's Hospital of Ludwig Maximilians University, Lindwurmstrasse 4, D-80337 Munich, Germany. mgriese@helios.med.uni-muenchen.de
Wiesener
A
A
Lottspeich
F
F
von Bredow
Ch
Ch
D000372:Agglutination Tests; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D037102:Lectins / Q000378:metabolism*; D019272:Leukocyte Elastase / Q000494:pharmacology; D008970:Molecular Weight; D011489:Protein Denaturation; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000276:immunology; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
D037102:Lectins; D037663:Pulmonary Surfactant-Associated Protein D; D011994:Recombinant Proteins; D019272:Leukocyte Elastase; D002118:Calcium