Binding of surfactant protein A to the lipid A moiety of bacterial lipopolysaccharides.
Surfactant protein A (SP-A) enhances the phagocytosis of opsonized and non-opsonized bacteria by alveolar macrophages, but it is not known with which component of the bacterial surface it associates. We investigated the interaction of SP-A with lipopolysaccharides (LPS), which are important biologically active constituents of the outer membranes of Gram-negative bacteria. Flow cytometry was used to study the binding of fluorescein isothiocyanate-labelled SP-A either to LPS of various chain lengths coupled to magnetic beads or to Gram-negative bacteria. The binding of SP-A to LPS-coated beads was saturable, both time- and concentration-dependent, and required both Ca2+ and Na+. SP-A bound to the lipid A moiety of LPS and to LPS from either the Re-mutant of Salmonella minnesota or the J5-mutant of Escherichia coli. In contrast, it did not bind to O111 LPS of E. coli, suggesting that SP-A binds only to rough LPS. The binding of SP-A to LPS was not affected by mannan and heparin or by deglycosylation of the SP-A, indicating that the carbohydrate-binding domain and the carbohydrate moiety of SP-A are not involved in its interaction with LPS. We also observed saturable and concentration-dependent binding of SP-A to the live J5 mutant of whole E. coli, but not to its O111 mutant. In addition, Re LPS aggregated in the presence of SP-A, Ca2+ and Na+. We conclude that SP-A associates with LPS via the lipid A moiety of rough LPS and may be involved in the anti-bacterial defences of the lung.
Laboratory of Veterinary Biochemistry, Utrecht, The Netherlands.
J F
JF
Van Iwaarden
J C
JC
Pikaar
J
J
Storm
E
E
Brouwer
J
J
Verhoef
R S
RS
Oosting
L M
LM
van Golde
J A
JA
van Strijp
D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D006801:Humans; D008050:Lipid A / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D008863:Microspheres; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D011510:Proteolipids / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D012475:Salmonella / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D008050:Lipid A; D008070:Lipopolysaccharides; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012964:Sodium; D016650:Fluorescein-5-isothiocyanate; D002118:Calcium