title: Heterogeneous MAC Initiator and Pore Structures in a Lipid Bilayer by Phase-Plate Cryo-electron Tomography.
abstract: Pore formation in membranes is important for mammalian immune defense against invading bacteria. Induced by complement activation, the membrane attack complex (MAC) forms through sequential binding and membrane insertion of C5b6, C7, C8, and C9. Using cryo-electron tomography with a Volta phase plate and subtomogram averaging, we imaged C5b-7, C5b-8, and C5b-9 complexes and determined the C5b-9 pore structure in lipid bilayers. The in situ C5b-9 pore structure at 2.3-nm resolution reveals a 10- to 11.5-nm cone-shaped pore starting with C5b678 and multiple copies of C9 that is poorly closed, yielding a seam between C9 and C6 substituting for the shorter β strands in C6 and C7. However, large variations of composite pore complexes are apparent in subtomograms. Oligomerized initiator complexes C5b-7 and C5b-8 show stages of membrane binding, deformation, and perforation that yield ∼3.5-nm-wide pores. These data indicate a dynamic process of pore formation that likely adapts to biological membranes under attack.
authors.affiliation: Section Electron Microscopy, Department of Molecular Cell Biology, Leiden University Medical Center, 2300 RC Leiden, the Netherlands. Electronic address: t.sharp@lumc.nl.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Sharp
authors.affiliation: Section Electron Microscopy, Department of Molecular Cell Biology, Leiden University Medical Center, 2300 RC Leiden, the Netherlands; NeCEN, Gorlaeus Laboratories, Leiden University, 2333 CC Leiden, the Netherlands.
authors.forename: Abraham J
authors.initials: AJ
authors.lastname: Koster
authors.affiliation: Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research and Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands. Electronic address: p.gros@uu.nl.
authors.forename: Piet
authors.initials: P
authors.lastname: Gros
mesh_terms: D015938:Complement Membrane Attack Complex / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D055032:Electron Microscope Tomography; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding
chemical_list: D015938:Complement Membrane Attack Complex; D008051:Lipid Bilayers
keywords: complement; electron tomography; membrane attack complex; membrane pore; phase plate; subtomogram average