Binding of FH20 to microbial proteins enhance the FH-C3b interaction.

<p>Panel <b>A</b> shows enhanced binding of radiolabeled FH19-20 to solid phase C3b in the presence of 1.25 µM OspE, FhbA, or Tuf compared to buffer control (cpm ±SD from a representative experiment performed in triplicates is shown; difference to the control was calculated by a t-test; *p<0.05, **p<0.01, ***p<0.001). In panel <b>B</b>, binding of ¹²⁵I-OspE to C3b (or bovine serum albumin, BSA, as a negative control) is shown in the presence or absence 1.25 µM of FH19-20 or FH19^Del-20 lacking the C3d binding site on FH domain 19 (cpm ±SD from a representative experiment performed in triplicates is shown). Panel C shows solvent accessible surface representation of a model of the tripartite complex between FH19-20, C3b, and a microbial protein on a microbial surface. Two projections with the microbial membrane lipid bilayer on the bottom are shown. Color code: C3b (2WII, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003308#ppat.1003308-Wu1" target="_blank">[44]</a>) is shown in blue and its C3d part (TED domain) is darker blue with the thioester site in orange (1C3d, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003308#ppat.1003308-Jokiranta2" target="_blank">[7]</a>); a microbial protein is shown in yellow; FH19-20 is shown in grey (2g7i, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003308#ppat.1003308-Kajander1" target="_blank">[8]</a>).