Binding of Streptococcal Lipoteichoic Acid to Fatty Acid-Binding Sites on Human Plasma Fibronectin

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Abstract
The ability of Streptococcus pyogenes lipoteichoic acid and palmitic acid to bind to purified human plasma fibronectin was investigated. Initial studies indicated that intact fibronectin formed soluble complexes with lipoteichoic acid, resulting in a change in the mobility of fibronectin in an electrical field. Fibronectin covalently linked to agarose beads bound radiolabeled lipoteichoic acid in the acylated, but not in the deacylated, form. An 18-M excess of fibronectin inhibited binding of lipoteichoic acid to the immobilized protein by 92%. Fibronectin-bound [3H]lipoteichoic acid could be specifically eluted with unlabeled lipoteichoic acid and by fatty acid-free serum albumin. Serum albumin, which is known to contain fatty acid-binding sites capable of binding to the lipid moieties of lipoteichoic acid, inhibited the binding of lipoteichoic acid to fibronectin in a competitive fashion. The fibronectin-bound lipoteichoic acid could be eluted by 50% ethanol and various detergents, but not by 1.0 M NaCl, various amino acids or sugars. Radiolabeled palmitic acid adsorbed to fibronectin could be eluted with 50% ethanol, but not with 1.0 M NaCl. Fibronectin adsorbed to a column of palmityl-Sepharose was eluted with 50% ethanol in 0.5% sodium dodecyl sulfate, but not with 1.0 M NaCl or 1% sodium dodecyl sulfate alone. The binding of lipoteichoic acid to fibronectin followed 1st-order kinetics and was saturable. A Scatchard plot analysis of the binding data indicated a heterogeneity of lipoteichoic acid-binding sites similar to that previously found for serum albumin. Fibronectin contains at least 1 population of high-affinity binding sites for lipoteichoic acid. The binding affinity (nKa .simeq. 250 .mu.M-1) is 2 orders of magnitude greater than the binding affinity of serum albumin. Human plasma fibronectin may contain specific binding sites for fatty acids, and lipoteichoic acid may bind to these sites by way of its glycolipid moiety.