Degradation of pulmonary surfactant protein D by Pseudomonas aeruginosa elastase abrogates innate immune function.
The alveolar epithelium is lined by surfactant, a lipoprotein complex that both reduces surface tension and mediates several innate immune functions including bacterial aggregation, alteration of alveolar macrophage function, and regulation of bacterial clearance. Surfactant protein-D (SP-D) participates in several of these immune functions, and specifically it enhances the clearance of the pulmonary pathogen Pseudomonas aeruginosa, a common cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa secretes a variety of virulence factors including elastase, a zinc-metalloprotease, which degrades both SP-A and SP-D. Here we show that SP-D is cleaved by elastase to produce a stable 35-kDa fragment in a time-, temperature-, and dose-dependent manner. Degradation is inhibited by divalent metal cations, a metal chelator, and the elastase inhibitor, phosphoramidon. Sequencing the SP-D degradation products localized the major cleavage sites to the C-terminal lectin domain. The SP-D fragment fails to bind or aggregate bacteria that are aggregated by intact SP-D. SP-D fragment is observed when normal rat bronchoalveolar lavage (BAL) is treated with Pseudomonas aeruginosa elastase, and SP-D fragments are present in the BAL of CF lung allograft patients. These data show that degradation of SP-D occurs in the BAL environment and that degradation eliminates many normal immune functions of SP-D.
Alcorn
John F
JF
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Wright
Jo Rae
JR
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001992:Bronchoalveolar Lavage Fluid; D002412:Cations; D002469:Cell Separation; D002614:Chelating Agents / Q000494:pharmacology; D002850:Chromatography, Gel; D003550:Cystic Fibrosis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004848:Epithelium / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D037102:Lectins / Q000737:chemistry; D008168:Lung / Q000166:cytology / Q000378:metabolism; D016040:Lung Transplantation; D008264:Macrophages / Q000378:metabolism; D008666:Metalloendopeptidases / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010587:Phagocytosis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011650:Pulmonary Alveoli / Q000378:metabolism; D037663:Pulmonary Surfactant-Associated Protein D / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D001426:Bacterial Proteins; D002412:Cations; D002614:Chelating Agents; D037102:Lectins; D037663:Pulmonary Surfactant-Associated Protein D; D011994:Recombinant Proteins; D008666:Metalloendopeptidases; C043859:pseudolysin, Pseudomonas aeruginosa