Human surfactant protein D (SP-D) binds Mycoplasma pneumoniae by high affinity interactions with lipids.
Increasing evidence now identifies surfactant protein D (SP-D) as an important element of the innate immune system of the lung. In this study, we examined the interactions of rat and human SP-D with the human pathogen, Mycoplasma pneumoniae. Rat and human SP-D bound the organism with high affinity in a reaction that required Ca(2+) and was inhibited by EGTA. Membranes derived from the organism bound the proteins in a similar manner, except the rat SP-D also exhibited a significant level of Ca(2+)-independent binding. Pretreatment of membranes with proteases did not alter the Ca(2+)-dependent SP-D binding of membranes by either protein. Mannose, glucose, maltose, and inositol, at millimolar concentrations, competed for human SP-D binding to the bacterial membrane. Lipids extracted from membranes and separated by two-dimensional thin layer chromatography bound human SP-D with high affinity in a Ca(2+)-dependent reaction. A tandem mutant of SP-D with E321Q and N323D substitutions, failed to bind M. pneumoniae lipids, directly implicating the carbohydrate recognition domain in the interaction. The interaction of rat and human SP-D with M. pneumoniae was unaffected by the presence of surfactant lipids and the hydrophobic surfactant proteins. These findings demonstrate that M. pneumoniae is likely to be recognized by SP-D in the alveolar environment and that primary determinants recognized on the organism are lipid components of the cell membrane.
Chiba
Hirofumi
H
Program in Cell Biology, Department of Medicine, National Jewish Medical and Research Center, Denver, Colorado 80206, USA.
Pattanajitvilai
Surapon
S
Evans
Amanda J
AJ
Harbeck
Ronald J
RJ
Voelker
Dennis R
DR
D000818:Animals; D001667:Binding, Competitive; D002855:Chromatography, Thin Layer; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D050356:Lipid Metabolism; D009177:Mycoplasma pneumoniae / Q000378:metabolism*; D011485:Protein Binding; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats
D006023:Glycoproteins; D008024:Ligands; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants