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Protein Targeting and Translocation

Protein Targeting and Translocation

Edited by D. A. Phoenix
Copyright Date: 1998
Pages: 304
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  • Book Info
    Protein Targeting and Translocation
    Book Description:

    Protein targeting is a fast-moving field that has encompassed areas from biophysics to molecular biology to try to gain insight into how proteins are directed to their final functional location and how such macromolecules are able to cross semi-permeable membrane barriers during their journey. This text reviews our current state of knowledge regarding the interaction of proteins at the membrane interface and the assembly of proteins into biological membranes, before proceeding to look at targeting pathways in both prokaryotic and eukaryotic systems. The reviews have been written by some of the leading researchers in the field, with contributions from around the world and with more than 1,800 references. The text is aimed at graduate students and at researchers with an interest in protein targeting, but may also be of use to final-year undergraduates.

    Originally published in 1998.

    ThePrinceton Legacy Libraryuses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

    eISBN: 978-1-4008-6501-7
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
  3. Preface
    (pp. vii-x)
  4. Abbreviations
    (pp. xi-xii)
  5. Membrane interactions

    • 1 Biophysics of the membrane interface and its involvement in protein targeting and translocation
      (pp. 1-18)
      A. Watts and T.J.T. Pinheiro

      The initial site of association for any component that may partition into and then, as one possibility, traverse a membrane is the polar/apolar interface of the membrane. Whether or not a protein or lipid acts as the target site, such associations are driven initially, and possibly subsequently, by electrostatic forces. These forces are important not only in ionic interactions and conductance effects, but also in determining the structure and activity of membrane proteins, including protein insertion and translocation [1–3]. Here, the relevant thermodynamic and electrostatic aspects of membrane protein association and insertion will be reviewed. As specific examples of...

    • 2 Amphiphilic α-helices and lipid interactions
      (pp. 19-36)
      David A. Phoenix and Frederick Harris

      Proteins and peptides that interact with membranes have to accommodate the amphiphilic nature of the bilayer, and to do so must either possess or be able to adopt amphiphilic architecture. On a structural basis these architectures may be classified as possessing primary, secondary or tertiary amphiphilicity, with each having a range of effects on membrane lipid organization.

      Primary amphiphilicity is typically found within the structures of integral membrane proteins, and is defined by transmembrane stretches of apolar residues which are terminated at the membrane surface by clusters of hydrophilic residues (see Chapters 4 and 5). It has been suggested that...

    • 3 Signal sequences: initiators of protein translocation
      (pp. 37-48)
      N. Nouwen, J. Tommassen and B. de Kruijff

      The cell envelope ofEnterobacteriaceae, such asEscherichia coli, consists of a cytoplasmic or inner membrane and an outer membrane, which are separated by the periplasm. Proteins that are localized in the periplasm or in the outer membrane have to be translocated across the inner membrane of the cell. These proteins are synthesized as precursors with an N-terminal extension, the signal sequence, which is essential for translocation across the inner membrane [1]. Genetic and biochemical studies on the translocation process inE. colihave led to the identification of several soluble and inner-membrane proteins, usually designated the Sec proteins, that...

    • 4 Determinants of membrane protein topology and membrane anchoring
      (pp. 49-66)
      Lida Hashemzadeh-Bonehi, Jansen P. Jacob, Costas Mitsopoulos and Jenny K. Broome-Smith

      Since membrane proteins inhabit the amphipathic environment of phospholipid bilayers, this imposes special constraints on their structures. Although the tertiary structures of few membrane proteins are known, it seems likely that, with the exception of the β-barrel type found in bacterial outer membranes, most consist of hydrophobic α-helical membrane-spanning segments (MSSs) connected by hydrophilic extramembranous domains. An α-helix of 20 amino acids should be long enough to span the lipid portion of the bilayer, and high-resolution structures of bacteriorhodopsin and bacterial photosynthetic reaction centres reveal multiple membrane-spanning hydrophobic α-helices of approximately this length (although some are substantially longer or shorter)...

    • 5 Insertion of single- and multi-spanning proteins into the bacterial cytoplasmic membrane
      (pp. 67-84)
      D. Kiefer and A. Kuhn

      Membrane proteins are designed so as to avoid rapid folding in the cytoplasm and to insert efficiently into the membrane of a cell. They follow an often complex pathway involving transient interaction with chaperone proteins, translocase components and phospholipid molecules, and after membrane insertion they may require assembly into a multimeric protein complex for activity (see Chapter 4). In addition to the more complex membrane assembly pathways, simple routes exist, particularly for small membrane proteins, in which the newly synthesized proteins interact directly with the membrane bilaver. Naturally, small proteins have less problems with misfolding in the cytoplasm and translocating...

  6. Prokaryotic protein targeting and translocation

    • 6 Prokaryotic protein translocation
      (pp. 85-104)
      Arnold J. M. Driessen

      In prokaryotes, proteins are exported across the cytoplasmic membrane and subsequently targeted to the periplasm, the outer membrane and/or the external medium. These proteins are synthesized at the ribosomes, mostly as cleavable signal-sequence-bearing precursors (see Chapter 3). The signal sequence acts as a targeting and recognition signal for the translocase, a complex of integral and peripheral membrane proteins that catalyses the energy-dependent translocation of preproteins across the cytoplasmic membrane (see also Chapter 7).

      During the past few years, our understanding of the mechanism of protein translocation has advanced rapidly withEscherichia colias a model organism. By ingenious genetic screening...

    • 7 Protein traffic from the cytosol to the outer membrane of Escherichia coli
      (pp. 105-120)
      H. Tokuda and S. Matsuyama

      Escherichia coli, a Gram-negative bacterium, consists of four compartments: the cytoplasm, the inner (cytoplasmic) membrane, the periplasm and the outer membrane. Proteins destined for the periplasm and outer membrane are synthesized as precursors with a signal peptide (Chapter 3) at their N-termini, and are then translocated across the cytoplasmic membrane by the translocase machinery (Chapter 6). The sorting and transport of translocated proteins subsequently takes placc, leading to their localization at the final destination, i.e. the periplasm or outer membrane.

      So far it has been revealed that seven factors (SecA, SecB, SecD, SecE, SecF, SecG and SecY) are involved in...

    • 8 sec-dependent prokaryotic protein secretion
      (pp. 121-142)
      J. D. Thomas, S. D. Wharam and G.P.C. Salmond

      Bacteria secrete a wide range of toxins, degradative enzymes and other virulence factors into the external milieu. In Gram-positive bacteria, secreted proteins only have to traverse one membrane (the cytoplasmic membrane) in order to reach the extracellular medium. In contrast, in Gram-negative bacteria, secreted proteins must cross the cell envelope, which comprises two membranes (inner/cytoplasmic and outer) and the periplasm.

      Gram-negative secretion processes can be categorized into at least three major, highly conserved, but functionally independent, translocation pathways, termed type I, type II or general secretion pathway (GSP), and type III. A few highly specialized secretion mechanisms which do not...

    • 9 Targeting and assembly of fimbriae
      (pp. 143-168)
      C.J. Smyth, S.G.J. Smith and M.B. Marron

      Colonization of an epithelial surface is a common initial event in bacterial pathogenesis. Host, tissue and cell specificity in attachment are conferred by surface-associated molecules termed adhesins. Bacterial fimbriae are one class of adhesins [1], These are rod-like structures of approx. 7 nm in diameter or flexible fibrils with a diameter of 2–5 nm which can be visualized on the bacterial surface by standard electron microscopic techniques. Non-fimbrial adhesins are not in general as well characterized. The recognition of receptor structures by adhesins accounts for selective interactions with the host and involves a stereochemical fit between the adhesin and...

  7. Eukaryotic protein targeting and translocation

    • 10 Targeting to and translocation across the endoplasmic reticulum membrane
      (pp. 169-192)
      Jeffrey L. Brodsky

      The biogenesis of secretory proteins begins with their insertion, or translocation, either into the lumen of the endoplasmic reticulum (ER) or into the lipid bilayer of the ER membrane. Consequently, protein translocation is the first committed step in the secretory pathway. Secreted proteins subsequently travel in vesicles that migrate sequentially from the ER to the Golgi complex, and finally to the plasma membrane, at which time they may be released from or retained in the plasma membrane. The secretory pathway also transports soluble and membrane proteins that may be withheld in the ER or Golgi complex (see Chapter 11).


    • 11 Protein localization to the endoplasmic reticulum and Golgi complex
      (pp. 193-212)
      R. Qanbar and C.E. Machamer

      Many specialized reactions in the cell occur in membrane-bounded compartments. This compartmentalization may serve a number of purposes, including the temporal and spatial isolation of specific reactions, the enclosure of potentially harmful enzymes (e.g. the hydrolases of the lysozome), the creation of specific micro-environmental conditions in which certain processes can take place and the concentration of specialized components to a region, or a combination of these functions. The targeting of resident proteins that perform compartment-specific functions is a major area of interest in cell biology.

      Proteins destined for export follow either the classical [1–3] or the non-classical [4] secretory...

    • 12 Import and export of proteins at the nucleus
      (pp. 213-230)
      Naoko Imamoto, Yoichi Miyamoto and Yoshihiro Yoneda

      Transport across the nuclear envelope, to a region where genes are sequestered in the nuclear compartment, is dissimilar to protein translocation across other types of biological membranes, such as mitochondria, endoplasmic reticulum and peroxisomes, in that transport occurs in both directions. Bidirectional transport provides an important avenue of communication between cytoplasm and nucleus. To enter and exit the nucleus, molecules translocate through a large proteinaceous structure called the nuclear pore complex (NPC), which spans the double lipid bilayer of the nuclear envelope (reviewed in [1–4]). This structure, of approx. 125 MDa, contains aqueous channels of 9 nm diameter that...

    • 13 Mitochondrial targeting and import
      (pp. 231-248)
      Ruud Hovius

      Mitochondria contain hundreds of different proteins, of which only a handful are encoded by the mitochondrial genome. Most of these mitochondrially encoded proteins are key components of the multisubunit complexes involved in oxidative phosphorylation. The majority of the nuclear-encoded proteins are synthesized in the cytosol on free polysomes and contain signals coding for their destination. They are complexed by cytosolic factors (chaperonins) and guided towards the mitochondria, where an intricate machinery takes care of import and correct sorting. The import of proteins into mitochondria is complex, since these organelles contain two membranes, enclosing between them the intermembrane space, with the...

    • 14 Translocation of proteins into and across the thylakoid membrane
      (pp. 249-258)
      Colin Robinson, Alexandra Mant and Susanne Brink

      Chloroplast biogenesis is a complex process, requiring protein trafficking on a massive scale. This organelle is one of the most complex known in structural terms, comprising three distinct membranes (outer and inner envelopes and the thylakoid membrane) that enclose, in turn, three distinct soluble phases (intermembrane space, stroma and thylakoid lumen). The chloroplast contains its own genetic system and synthesizes about 10–20% of the organellar proteins; the remainder are imported after synthesis in the cytosol. In total, several hundred different proteins are imported from the cytosol and distributed to all six chloroplastic subcompartments; hence the processes of protein import...

    • 15 Principles of peroxisomal protein sorting and assembly
      (pp. 259-272)
      J.A.K.W. Kiel, I.J. van der Klei and M. Veenhuis

      Microbodies (peroxisomes/glyoxysomes/glycosomes) are currently recognized as a class of important organelles, indispensable for the proper functioning of eukaryotic cells. Although their morphological structure is relatively simple, their physiological properties are remarkably complex. Initially, the organelles were thought to be involved in hydrogen peroxide generation and decomposition, Subsequently, various microbody functions have been described, including essential roles in photorespiration in plants, cholesterol metabolism and plasmalogen biosynthesis in mammals, penicillin biosynthesis in filamentous fungi, and C₁ and C₂ metabolism in fungi [1,2], Part of the problem in assigning a single function to the compartment is that the menu of peroxisomal proteins varies...

    • 16 Targeting of glyoxysomal proteins
      (pp. 273-286)
      A. Baker and B. Tugal

      ‘Peroxisomes’ or ‘microbodies’ is a general term used to describe a class of organelles that are bounded by a single membrane bilayer, possess flavin-containing oxidases which generate hydrogen peroxide, and also contain catalase (EC, which degrades generated hydrogen peroxide ([1]; Chapter 15). Glyoxysomcs are a specialized type of peroxisome that are defined by the presence of the glyoxylate pathway enzymes in the lumen [2], In addition, glyoxysomes (and other types of peroxisomes) contain enzymes which break down fatty acids to acetyl-CoA (β-oxidation). Glyoxysomes are present in the cotyledons or endosperm tissue of oilstoring plant species, and in some fungi...

  8. Subject index
    (pp. 287-292)