Human FH binds to the HVR of the M5 and M6 proteins.

<p>(<b>A</b>) Binding of human FH to chromosomal mutants of the M5 strain. The upper part of the panel shows the location of deletions (ΔN1, ΔN2, ΔB and ΔC) causing the surface expression of truncated M5 proteins, and the positions of A, B and C repeats in M5. The lower part of the panel shows results of binding tests with pure FH and the mutants expressing truncated M5 proteins. The wild type M5 strain and a strain (ΔM5) lacking the entire M5 protein were also included. In the binding tests, pure FH was incubated with a suspension of the strain indicated. After washes, bound protein was eluted from the bacteria and analyzed by western blot, employing anti-FH for detection. Pure FH was included as a control in the blot (right). (<b>B</b> and <b>C</b>) Binding of FH to purified derivatives of the M5 protein (B) and the M6 protein (C). The proteins indicated were used to coat microtiter wells, using 0.1 µg per well, and analyzed for ability to bind pure FH, added at the concentration indicated. In B, wild type M5 protein was compared with two M5 derivatives (M5Δ80-86 and M5Δ87-93) with short deletions in the HVR, as indicated. In C, wild type M6 protein was compared with a deletion derivative having a short deletion in the HVR (M6Δ97-110), and with a dimerized construct derived from the C repeat region of M6 (M6-Crep), as indicated. (<b>D</b> and <b>E</b>) Binding of FH to whole <i>S. pyogenes</i> M5 bacteria (D) or M6 bacteria (E), and to bacterial mutants of these strains lacking C repeats (M5ΔC and M6ΔC) or no M protein (ΔM5 and ΔM6).