Fig. 2 | Nature Communications

Fig. 2

From: Single-molecule kinetics of pore assembly by the membrane attack complex

Fig. 2

C5b-7 initiates MAC formation and recruits C8 and C9 directly from solution. Binding of complement components C5b6, C7 and C8 to supported bacterial model membranes containing PG lipids, as observed by AFM and QCM-D. a AFM images increasingly show protruding features upon addition of C5b6, C7 and C8 to a bilayer formed of DOPE:DOPG (50:50 mol%). Scale bar: 200 nm, height scale: 1 nm. b QCM-D binding assay following the addition of complement proteins, in reverse sequence followed by the forward sequence, to a lipid bilayer formed of DOPC:DOPE:DOPG (47.5:47.5:5 mol%) on a silicon dioxide coated QCM-D sensor. In isolation, complement proteins C7, C8 and C9 do not bind to the membrane, requiring C5b6 to initiate the interaction. Distinct steps in both frequency (Δf) and dissipation (ΔD) upon sequential addition of C5b-7, C8 and C9 demonstrate protein binding to the membrane; wash steps (denoted by dotted red lines) between additions do not lead to a reduction in the signal size, revealing that the protein binding is stable. The dissipation shift increases upon binding, reflecting the relative softness of the protein complexes in the lipid bilayer film

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