title: Three-dimensional electron microscopic imaging of membrane invaginations in Escherichia coli overproducing the chemotaxis receptor Tsr.
abstract: Electron tomography is a powerful method for determining the three-dimensional structures of large macromolecular assemblies, such as cells, organelles, and multiprotein complexes, when crystallographic averaging methods are not applicable. Here we used electron tomographic imaging to determine the molecular architecture of Escherichia coli cells engineered to overproduce the bacterial chemotaxis receptor Tsr. Tomograms constructed from fixed, cryosectioned cells revealed that overproduction of Tsr led to formation of an extended internal membrane network composed of stacks and extended tubular structures. We present an interpretation of the tomogram in terms of the packing arrangement of Tsr using constraints derived from previous X-ray and electron-crystallographic studies of receptor clusters. Our results imply that the interaction between the cytoplasmic ends of Tsr is likely to stabilize the presence of the membrane networks in cells overproducing Tsr. We propose that membrane invaginations that are potentially capable of supporting axial interactions between receptor clusters in apposing membranes could also be present in wild-type E. coli and that such receptor aggregates could play an important role in signal transduction during bacterial chemotaxis.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20817, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lefman
authors.forename: Peijun
authors.initials: P
authors.lastname: Zhang
authors.forename: Teruhisa
authors.initials: T
authors.lastname: Hirai
authors.forename: Robert M
authors.initials: RM
authors.lastname: Weis
authors.forename: Jemma
authors.initials: J
authors.lastname: Juliani
authors.forename: Donald
authors.initials: D
authors.lastname: Bliss
authors.forename: Martin
authors.initials: M
authors.lastname: Kessel
authors.forename: Erik
authors.initials: E
authors.lastname: Bos
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Peters
authors.forename: Sriram
authors.initials: S
authors.lastname: Subramaniam
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure*; D002633:Chemotaxis; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure*; D005818:Genetic Engineering / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D014054:Tomography / Q000379:methods*; D015854:Up-Regulation
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; C057635:Tsr protein, Bacteria