Biology subjects

Menny, A.

Publications and source records attributed to Menny, A..

4 recordsLinked to original sources

bioRxiv2021

Structural basis for how sMAC is packaged for clearance

Unregulated complement activation causes inflammatory and immunological pathologies with consequences for human disease. To prevent bystander damage during an immune response, extracellular chaperones (clusterin and vitronectin) capture and clear soluble precursors to the membrane attack complex (sMAC). However, how these chaperones block further polymerization of MAC and prevent the complex from binding target membranes remains unclear. Here, we address that question by combining cryo electron microscopy (cryoEM) and cross-linking mass spectrometry (XL-MS) to solve the structure of sMAC. Together our data reveal how clusterin recognizes and inhibits polymerizing complement proteins by binding a negatively charged surface of sMAC. Furthermore, we show that the pore-forming C9 protein is trapped in an intermediate conformation whereby only one of its two transmembrane {beta}-hairpins has unfurled. This structure provides molecular details for immune pore formation and helps explain a complement control mechanism that has potential implications for how cell clearance pathways mediate immune homeostasis.

biophysics↗

bioRxiv2020

Mutational analysis to explore long-range allosteric coupling and decoupling in a pentameric channel receptor

Pentameric ligand-gated ion channels (pLGICs) mediate chemical signaling through a succession of allosteric transitions that are yet not completely understood. On the prototypic bacterial channel GLIC, we explored the conformational landscape of the protein during pH-gating. To this aim, we introduced a series of allosteric mutations, and characterized the protein conformation over a broad pH range. We combined electrophysiological recordings, fluorescence quenching experiments monitoring key quaternary reorganizations, and simulations by normal mode analysis. Moderate loss-of-function mutations and the allosteric modulator propofol displace allosteric equilibria involved in pre-activation and pore opening processes, highlighting long-range allosteric coupling between distant regions of the protein. In contrast, total loss-of-function mutations stabilize the protein in unique intermediate conformations where motions are decoupled. Altogether, our data show that the protein can access a wide conformational landscape, raising the possibility of multiple conformational pathways during gating.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗

bioRxiv2018

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

The membrane attack complex (MAC) is a hetero-oligomeric protein assembly that kills pathogens by perforating their cell envelopes. The MAC is formed by sequential assembly of soluble complement proteins C5b, C6, C7, C8 and C9, but little is known about the rate-limiting steps in this process. Here, we use rapid atomic force microscopy (AFM) imaging to show that MAC proteins oligomerize within the membrane, unlike structurally homologous bacterial pore-forming toxins. C5b6 interacts with the lipid bilayer prior to recruiting C7 and C8. We discover that incorporation of the first C9 is the kinetic bottleneck of MAC formation, after which rapid C9 oligomerization completes the pore. This defines the kinetic basis for MAC assembly and provides insight into how human cells are protected from bystander damage by the cell surface receptor CD59, which is offered a maximum temporal window to halt the assembly at the point of C9 insertion.

biophysics↗

bioRxiv2018

CryoEM reveals how the complement membrane attack complex ruptures lipid bilayers

The membrane attack complex (MAC) is one of the immune systems first responders. Complement proteins assemble on target membranes to form pores that lyse pathogens and impact tissue homeostasis of self-cells. How MAC disrupts the membrane barrier remains unclear. Here we use electron cryo-microscopy and flicker spectroscopy to show that MAC interacts with lipid bilayers in two distinct ways. Whereas C6 and C7 associate with the outer leaflet and reduce the energy for membrane bending, C8 and C9 traverse the bilayer increasing membrane rigidity. CryoEM reconstructions reveal plasticity of the MAC pore and demonstrate how C5b6 acts as a platform, directing assembly of a giant {beta}-barrel whose structure is supported by a glycan scaffold. Our work provides a structural basis for understanding how {beta}-pore forming proteins breach the membrane and reveals a mechanism for how MAC kills pathogens and regulates cell functions.

biophysics↗