N-Terminally Extended Surfactant Protein (SP) C Isolated from SP-B-Deficient Children Has Reduced Surface Activity and Inhibited Lipopolysaccharide Binding

• Published in: Biochemistry (Easton) 2004-04, Vol.43 (13), p.3891-3898
• Main Authors: Li, Jing, Ikegami, Machiko, Na, Cheng-Lun, Hamvas, Aaron, Espinassous, Quentin, Chaby, Richard, Nogee, Lawrence M, Weaver, Timothy E, Johansson, Jan
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Bronchoalveolar Lavage Fluid - chemistry; Child; Chromatography, High Pressure Liquid; Homozygote; Humans; Lipopolysaccharides - antagonists & inhibitors; Lipopolysaccharides - metabolism; Lung - chemistry; Medicin och hälsovetenskap; Mice; Mice, Transgenic; Molecular Sequence Data; Mutation; Peptide Fragments - isolation & purification; Peptide Fragments - metabolism; Peptide Fragments - secretion; Protein Binding; Protein Precursors - isolation & purification; Protein Precursors - metabolism; Protein Precursors - secretion; Protein Processing, Post-Translational; Pulmonary Surfactant-Associated Protein B - deficiency; Pulmonary Surfactant-Associated Protein B - genetics; Pulmonary Surfactant-Associated Protein C - isolation & purification; Pulmonary Surfactant-Associated Protein C - metabolism; Pulmonary Surfactant-Associated Protein C - secretion; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Surface Properties; Swine
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi036218q

In both humans and mice, a deficiency of surfactant protein B (SP-B) is associated with a decreased concentration of mature SP-C and accumulation of a larger SP-C peptide, denoted SP-Ci, which is not observed under normal conditions. Isolation of hydrophobic polypeptides from the lungs of children who died with two different SP-B mutations yielded pure SP-Ci and showed only trace amounts of mature SP-C. Determination of the SP-Ci covalent structure revealed a 12-residue N-terminal peptide segment, followed by a 35-residue segment that is identical to mature SP-C. The SP-Ci structure determined herein is similar to that of a proposed late intermediate in the processing of proSP-C, suggesting that SP-Ci is the immediate precursor of SP-C. In bronchoalveolar lavage fluid from transgenic mice with a focal deficiency of SP-B, SP-Ci was detected in the biophysically active, large aggregate fraction and was associated with membrane structures that are typical for a large aggregate surfactant. However, unlike SP-C, SP-Ci exhibited a very poor ability to promote phospholipid adsorption, gave high surface tension during cyclic film compression, and did not bind lipopolysaccharide in vitro. SP-Ci is thus capable of associating with surfactant lipids, but its N-terminal dodecapeptide segment must be proteolytically removed to generate a biologically functional peptide. The results of this study indicate that the early postnatal fatal respiratory distress seen in SP-B-deficient children is combined with the near absence of active variants of SP-C.