title: Membrane invagination induced by Shiga toxin B-subunit: from molecular structure to tube formation.
abstract: The bacterial Shiga toxin is composed of an enzymatically active A-subunit, and a receptor-binding homopentameric B-subunit (STxB) that mediates intracellular toxin trafficking. Upon STxB-mediated binding to the glycolipid globotriaosylceramide (Gb3) at the plasma membrane of target cells, Shiga toxin is internalized by clathrin-dependent and independent endocytosis. The formation of tubular membrane invaginations is an essential step in the clathrin-independent STxB uptake process. However, the mechanism by which STxB induces these invaginations has remained unclear. Using a combination of all-atom molecular dynamics and Monte Carlo simulations we show that the molecular architecture of STxB enables the following sequence of events: the Gb3 binding sites on STxB are arranged such that tight avidity-based binding results in a small increment of local curvature. Membrane-mediated clustering of several toxin molecules then creates a tubular membrane invagination that drives toxin entry into the cell. This mechanism requires: (1) a precise molecular architecture of the STxB binding sites; (2) a fluid bilayer in order for the tubular invagination to form. Although, STxB binding to the membrane requires specific interactions with Gb3 lipids, our study points to a generic molecular design principle for clathrin-independent endocytosis of nanoparticles.
authors.affiliation: Center for Biomembrane Physics (MEMPHYS), Department of Physics, Chemistry and Pharmacy (FKF), University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark. ipsen@memphys.sdu.dk.
authors.forename: W
authors.initials: W
authors.lastname: Pezeshkian
authors.forename: A G
authors.initials: AG
authors.lastname: Hansen
authors.forename: L
authors.initials: L
authors.lastname: Johannes
authors.forename: H
authors.initials: H
authors.lastname: Khandelia
authors.forename: J C
authors.initials: JC
authors.lastname: Shillcock
authors.forename: P B S
authors.initials: PB
authors.lastname: Kumar
authors.forename: J H
authors.initials: JH
authors.lastname: Ipsen
mesh_terms: D001665:Binding Sites; D002462:Cell Membrane; D004705:Endocytosis; D015394:Molecular Structure; D021381:Protein Transport; D022621:Shiga Toxin / Q000737:chemistry*; D014281:Trihexosylceramides / Q000737:chemistry*
chemical_list: D014281:Trihexosylceramides; C018549:globotriaosylceramide; D022621:Shiga Toxin