Myeloperoxidase-dependent inactivation of surfactant protein D in vitro and in vivo.
Surfactant protein D (SP-D) plays diverse and important roles in innate immunity and pulmonary homeostasis. Neutrophils and myeloperoxidase (MPO) colocalized with SP-D in a murine bacterial pneumonia model of acute inflammation, suggesting that MPO-derived reactive species might alter the function of SP-D. Exposure of SP-D to the complete MPO-H(2)O(2)-halide system caused loss of SP-D-dependent aggregating activity. Hypochlorous acid (HOCl), the major oxidant generated by MPO, caused a similar loss of aggregating activity, which was accompanied by the generation of abnormal disulfide-cross-linked oligomers. A full-length SP-D mutant lacking N-terminal cysteine residues and truncation mutants lacking the N-terminal domains were resistant to the oxidant-induced alterations in disulfide bonding. Mass spectroscopy of HOCl-treated human SP-D demonstrated several modifications, but none involved key ligand binding residues. There was detectable oxidation of cysteine 15, but no HOCl-induced cysteine modifications were observed in the C-terminal lectin domain. Together, the findings localize abnormal disulfide cross-links to the N-terminal domain. MPO-deficient mice showed decreased cross-linking of SP-D and increased SP-D-dependent aggregating activity in the pneumonia model. Thus, MPO-derived oxidants can lead to modifications of SP-D structure with associated alterations in its characteristic aggregating activity.
Department of Pathology and Immunology, Washington University School of Medicine, Saint Louis, Missouri 63110, USA. crouch@path.wustl.edu
Erika C
EC
Crouch
Tim O
TO
Hirche
Baohai
B
Shao
Rachel
R
Boxio
Julien
J
Wartelle
Rym
R
Benabid
Barbara
B
McDonald
Jay
J
Heinecke
Sadis
S
Matalon
Azzaq
A
Belaaouaj
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003545:Cysteine / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D007249:Inflammation; D037102:Lectins / Q000737:chemistry; D008168:Lung / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D051379:Mice; D009195:Peroxidase / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry*; D051381:Rats
D004220:Disulfides; D037102:Lectins; D037663:Pulmonary Surfactant-Associated Protein D; D009195:Peroxidase; D003545:Cysteine