Abstract
Type 1 fimbriated (mannose-specific) Escherichia coli cells bind to mannose residues on human polymorphonuclear leukocytes (PMN); this leads to phagocytosis of the bacteria. To identify the mannose-containing receptors on the PMN, the cells were surface labeled with 125I and lysed in 0.5% Nonidet P-40, and the lysate was fractionated by affinity chromatography on a column of Sepharose-bound fimbriae. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of the material eluted from the column with 500 mM methyl-alpha-mannoside revealed two radioactive bands of Mr 70,000 to 80,000 (gp70-80) and 100,000 (gp100). Another weak band of Mr 150,000 (gp150) was observed after prolonged exposure of the gel. Upon blotting of the glycoproteins separated by polyacrylamide gel electrophoresis and overlaying of the blots with concanavalin A, gp150 appeared as the major band. Membrane preparations of the PMN were enriched in gp70-80, gp100, and gp150, in comparison with the cell homogenates, further suggesting that these glycoproteins are surface components. Fractionation of the membrane preparations on the immobilized fimbriae followed by concanavalin A overlay of blots of the methyl-alpha-mannoside-eluted material revealed that gp150 was the major component in this fraction. The eluted fraction, obtained from a cell lysate (4.4 micrograms/ml), inhibited by 70% the agglutination of yeasts by the intact bacteria. Our results suggest that the three surface glycoproteins isolated by us serve as receptors for mannose-specific E. coli on PMN and may be involved in the lectin-mediated phagocytosis of the bacteria.