soluble inhibited mac complex  (SMAC Corp)

Journal: Nature Communications

Article Title: Structural basis for membrane attack complex inhibition by CD59

doi: 10.1038/s41467-023-36441-z

Figure Lengend Snippet: The MAC pore is formed from the sequential and stepwise assembly of complement proteins: C5b, grey; C6, blue; C7, orange; C8α, pink; C8β, magenta; C8γ, light purple; C9, alternating monomers are yellow and green. During assembly, complement proteins undergo dramatic structural re-arrangements in which two helical bundles within their MACPF domains unfurl into membrane-inserting β-hairpins. CD59 (cyan) binds at two stages of this assembly process (C5b8 and C5b9) to block membrane perforation and C9 polymerization. Images are rendered from structural models. C5b6 and all MAC assemblies: PDB ID: 6H03 ; Soluble forms of complement proteins are derived from C6: PDB ID: 3T5O ; C8: PDB ID: 3OJY ; C9: PDB ID: 6CXO . C7 was derived from an AlphaFold2 prediction: AlphaFold Protein Structure Database P10643 .

Article Snippet: Here, only TMH1 has unfurled while TMH2 remains helical (Fig. ), similar to the terminal C9 of the soluble inhibited MAC (sMAC) complex .

Techniques: Membrane, Blocking Assay, Derivative Assay

Journal: Nature Communications

Article Title: Structural basis for membrane attack complex inhibition by CD59

doi: 10.1038/s41467-023-36441-z

Figure Lengend Snippet: A , B Cholesterol depletion assays. A representative image (out of 10 randomly selected locations) for each condition is shown. Scale bars, 50 μm. A Complement was activated on CHO cells with a polyclonal anti-CHO IgG antibody. Cells were incubated with C9-depleted human serum supplemented with a chemically labeled fluorescent C9 (C9-Alexafluor 568) capable of forming MAC. B CHO cells treated with MβCD to deplete cholesterol. Complement activation and C9 detection is as described in ( A ). Insets show a zoomed in view of single cell. Cartoon schematics highlight the pattern of MAC deposition. C CryoEM map of the C5b9 2 -CD59 complex in a lipid nanodisc applying a positive B-factor of +50 Å 2 (transparent surface). Surface rendering of the protein model is underlayed. CD59 is cyan, C8β is magenta and the remaining complement proteins are grey. D Map generated from the coarse-grained model of the C5b8-CD59 complex including the GPI anchor (green). Protein components colored as in panel ( C ). Water molecules in proximity to the membrane are shown as blue spheres. Initial and final configurations for the three MD repeats are included in the Supplementary Data Files.

Article Snippet: Here, only TMH1 has unfurled while TMH2 remains helical (Fig. ), similar to the terminal C9 of the soluble inhibited MAC (sMAC) complex .

Techniques: Incubation, Labeling, Activation Assay, Generated, Membrane

Journal: Nature Communications

Article Title: Structural basis for membrane attack complex inhibition by CD59

doi: 10.1038/s41467-023-36441-z

Figure Lengend Snippet: A MAC assembles on cholesterol-rich microdomains (red hexagons) in the plasma membrane. While C7 anchors the growing MAC, C8β thins the bilayer and primes the membrane for rupture by C8α (pink). C9 joins the assembly, undergoing discrete structural transitions to form the pore. The MACPF domain of soluble C9 makes an initial contact and aligns the central β-sheet. The pore-forming β-hairpins extend sequentially. TMH1 is followed by TMH2, which allow C9 polymerization to complete the MAC pore. B CD59 is a GPI-anchored cell surface receptor that clusters in cholesterol-rich microdomains. Upon complement activation, CD59 could respond to membrane thinning by C8β and capture C8α as its transmembrane β-hairpins are extending (pink). While bound to C8α, CD59 is positioned to deflect the cascading C9 β-hairpins and divert their membrane trajectory (green). The next C9 molecule (yellow) is able to bind but trapped in an intermediate conformation in which TMH2 remains helical (red) and in which C9 polymerization is halted.

Article Snippet: Here, only TMH1 has unfurled while TMH2 remains helical (Fig. ), similar to the terminal C9 of the soluble inhibited MAC (sMAC) complex .

Techniques: Clinical Proteomics, Membrane, Cell Surface Receptor Assay, Activation Assay