Degradation of pulmonary surfactant protein D by Pseudomonas aeruginosa elastase abrogates innate immune function.

Abstract

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.

• Authors: John F Alcorn, Jo Rae Wright
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 279 Issue 29 Pg. 30871-9 (Jul 16 2004) ISSN: 0021-9258 [Print] United States
• PMID: 15123664 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Bacterial Proteins
• Cations
• Chelating Agents
• Lectins
• Pulmonary Surfactant-Associated Protein D
• Recombinant Proteins
• Metalloendopeptidases
• pseudolysin, Pseudomonas aeruginosa

Topics

• Amino Acid Sequence
• Animals
• Bacterial Proteins (chemistry, metabolism)
• Bronchoalveolar Lavage Fluid
• Cations
• Cell Separation
• Chelating Agents (pharmacology)
• Chromatography, Gel
• Cystic Fibrosis (metabolism)
• Dose-Response Relationship, Drug
• Epithelium (metabolism)
• Flow Cytometry
• Humans
• Lectins (chemistry)
• Lung (cytology, metabolism)
• Lung Transplantation
• Macrophages (metabolism)
• Metalloendopeptidases (chemistry, metabolism)
• Molecular Sequence Data
• Phagocytosis
• Protein Binding
• Protein Structure, Tertiary
• Pulmonary Alveoli (metabolism)
• Pulmonary Surfactant-Associated Protein D (metabolism)
• Rats
• Recombinant Proteins (metabolism)
• Salmonella typhimurium (metabolism)
• Temperature
• Time Factors