scholarly journals Implications for tetraspanin-enriched microdomain assembly based on structures of CD9 with EWI-F

2020 ◽  
Vol 3 (11) ◽  
pp. e202000883
Author(s):  
Wout Oosterheert ◽  
Katerina T Xenaki ◽  
Viviana Neviani ◽  
Wouter Pos ◽  
Sofia Doulkeridou ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Proteins ◽  
Crystal Structures ◽  
Transmembrane Helix ◽  
Extracellular Loop ◽  
Large Extracellular Loop ◽  
Ca 50 ◽  
Eukaryotic Membrane Proteins

Tetraspanins are eukaryotic membrane proteins that contribute to a variety of signaling processes by organizing partner-receptor molecules in the plasma membrane. How tetraspanins bind and cluster partner receptors into tetraspanin-enriched microdomains is unknown. Here, we present crystal structures of the large extracellular loop of CD9 bound to nanobodies 4C8 and 4E8 and, the cryo-EM structure of 4C8-bound CD9 in complex with its partner EWI-F. CD9–EWI-F displays a tetrameric arrangement with two central EWI-F molecules, dimerized through their ectodomains, and two CD9 molecules, one bound to each EWI-F transmembrane helix through CD9-helices h3 and h4. In the crystal structures, nanobodies 4C8 and 4E8 bind CD9 at loops C and D, which is in agreement with the 4C8 conformation in the CD9–EWI-F complex. The complex varies from nearly twofold symmetric (with the two CD9 copies nearly anti-parallel) to ca. 50° bent arrangements. This flexible arrangement of CD9–EWI-F with potential CD9 homo-dimerization at either end provides a “concatenation model” for forming short linear or circular assemblies, which may explain the occurrence of tetraspanin-enriched microdomains.

scholarly journals Implications for tetraspanin-enriched microdomain assembly based on structures of CD9 with EWI-F

2020 ◽  
Author(s):  
Wout Oosterheert ◽  
Katerina T. Xenaki ◽  
Viviana Neviani ◽  
Wouter Pos ◽  
Sofia Doulkeridou ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Proteins ◽  
Crystal Structures ◽  
Transmembrane Helix ◽  
Extracellular Loop ◽  
Parallel Orientation ◽  
D Loop ◽  
Large Extracellular Loop ◽  
Ca 50 ◽  
Eukaryotic Membrane Proteins

AbstractTetraspanins are ubiquitous eukaryotic membrane proteins that contribute to a variety of signaling processes by spatially organizing partner-receptor molecules in the plasma membrane. How tetraspanins bind and cluster partner receptors into so-called tetraspanin-enriched microdomains is unknown. Here we present crystal structures of the large extracellular loop of CD9 in complex with nanobodies 4C8 and 4E8; and, the cryo-EM structure of 4C8-bound CD9 in complex with its prototypical partner EWI-F. The CD9 - EWI-F complex displays a tetrameric arrangement with two centrally positioned EWI-F molecules, dimerized through their ectodomains, and two CD9 molecules, one bound to each EWI-F single-pass transmembrane helix through CD9-helices h3 and h4. In the crystal structures, nanobodies 4C8 and 4E8 bind CD9 at the C and D loop, in agreement with 4C8 binding at the ends of the CD9 - EWI-F cryo-EM complex. Overall, the 4C8 - CD9 - EWI-F - EWI-F - CD9 - 4C8 complexes varied from nearly two-fold symmetric (i.e. with the two CD9 - 4C8 copies in nearly anti-parallel orientation) to ca. 50° bent arrangements. Since membrane helices h1 and h2 and the EC2 D-loop have been previously identified as sites for tetraspanin homo-dimerization, the observed linear but flexible arrangement of CD9 - EWI-F with potential CD9 - CD9 homo-dimerization at either end provides a new ‘concatenation model’ for forming short linear or circular assemblies, which may explain the occurrence of tetraspanin-enriched microdomains.

scholarly journals Classes of non-conventional tetraspanins defined by alternative splicing

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Nikolas Hochheimer ◽  
Ricarda Sies ◽  
Anna C. Aschenbrenner ◽  
Dirk Schneider ◽  
Thorsten Lang
Keyword(s):  
Alternative Splicing ◽  
Membrane Proteins ◽  
Membrane Topology ◽  
Gene Products ◽  
Extracellular Loop ◽  
Transmembrane Topology ◽  
Transmembrane Segments ◽  
Structural Variability ◽  
Large Extracellular Loop

Abstract Tetraspanins emerge as a family of membrane proteins mediating an exceptional broad diversity of functions. The naming refers to their four transmembrane segments, which define the tetraspanins‘ typical membrane topology. In this study, we analyzed alternative splicing of tetraspanins. Besides isoforms with four transmembrane segments, most mRNA sequences are coding for isoforms with one, two or three transmembrane segments, representing structurally mono-, di- and trispanins. Moreover, alternative splicing may alter transmembrane topology, delete parts of the large extracellular loop, or generate alternative N- or C-termini. As a result, we define structure-based classes of non-conventional tetraspanins. The increase in gene products by alternative splicing is associated with an unexpected high structural variability of tetraspanins. We speculate that non-conventional tetraspanins have roles in regulating ER exit and modulating tetraspanin-enriched microdomain function.

Changes Occur in Plasma Membrane Turnover when K562 Leukemia Cells are Induced to Differentiate

1982 ◽  
Vol 40 ◽  
pp. 286-287
Author(s):  
L. M. Marshall
Keyword(s):  
Plasma Membrane ◽  
Membrane Proteins ◽  
Intracellular Transport ◽  
Parent Cell ◽  
Membrane Turnover ◽  
Coated Pits ◽  
Surface Distribution ◽  
Specific Proteins ◽  
Erythroleukemic Cell ◽  
Specific Membrane

A human erythroleukemic cell line, metabolically blocked in a late stage of erythropoiesis, becomes capable of differentiation along the normal pathway when grown in the presence of hemin. This process is characterized by hemoglobin synthesis followed by rearrangement of the plasma membrane proteins and culminates in asymmetrical cytokinesis in the absence of nuclear division. A reticulocyte-like cell buds from the nucleus-containing parent cell after erythrocyte specific membrane proteins have been sequestered into its membrane. In this process the parent cell faces two obstacles. First, to organize its erythrocyte specific proteins at one pole of the cell for inclusion in the reticulocyte; second, to reduce or abolish membrane protein turnover since hemoglobin is virtually the only protein being synthesized at this stage. A means of achieving redistribution and cessation of turnover could involve movement of membrane proteins by a directional lipid flow. Generation of a lipid flow towards one pole and accumulation of erythrocyte-specific membrane proteins could be achieved by clathrin coated pits which are implicated in membrane endocytosis, intracellular transport and turnover. In non-differentiating cells, membrane proteins are turned over and are random in surface distribution. If, however, the erythrocyte specific proteins in differentiating cells were excluded from endocytosing coated pits, not only would their turnover cease, but they would also tend to drift towards and collect at the site of endocytosis. This hypothesis requires that different protein species are endocytosed by the coated vesicles in non-differentiating than by differentiating cells.

Detergent fractionation with subsequent subtractive suppression hybridization as a tool for identifying genes coding for plasma membrane proteins

2009 ◽  
Vol 18 (6) ◽  
pp. 527-535 ◽  
Author(s):  
Andreas Lange ◽  
Claudia Kistler ◽  
Tanja B. Jutzi ◽  
Alexandr V. Bazhin ◽  
Claus Detlev Klemke ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Proteins ◽  
Plasma Membrane Proteins ◽  
Subtractive Suppression Hybridization

Specificity and promiscuity in membrane helix interactions

1994 ◽  
Vol 27 (2) ◽  
pp. 157-218 ◽  
Author(s):  
Mark A. Lemmon ◽  
Donald M. Engelman
Keyword(s):  
Membrane Proteins ◽  
Transmembrane Helix ◽  
Integral Membrane Proteins ◽  
Lipid Packing ◽  
Membrane Protein Folding ◽  
Membrane Spanning ◽  
Α Helix ◽  
Prosthetic Groups ◽  
Packing Effects ◽  
Helix Interactions

The membrane-spanning portions of many integral membrane proteins consist of one or a number of transmembrane α-helices, which are expected to be independently stable on thermodynamic grounds. Side-by-side interactions between these transmembrane α-helices are important in the folding and assembly of such integral membrane proteins and their complexes. In considering the contribution of these helix–helix interactions to membrane protein folding and oligomerization, a distinction between the energetics and specificity should be recognized. A number of contributions to the energetics of transmembrane helix association within the lipid bilayer will be relatively non-specific, including those resulting from charge–charge interactions and lipid–packing effects. Specificity (and part of the energy) in transmembrane α-helix association, however, appears to rely mainly upon a detailed stereochemical fit between sets of dynamically accessible states of particular helices. In some cases, these interactions are mediated in part by prosthetic groups.

scholarly journals Septin-dependent compartmentalization of the endoplasmic reticulum during yeast polarized growth

2005 ◽  
Vol 169 (6) ◽  
pp. 897-908 ◽  
Author(s):  
Cosima Luedeke ◽  
Stéphanie Buvelot Frei ◽  
Ivo Sbalzarini ◽  
Heinz Schwarz ◽  
Anne Spang ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Proteins ◽  
Diffusion Barriers ◽  
Yeast Cells ◽  
Dependent Manner ◽  
Protein Diffusion ◽  
Ultrastructural Studies ◽  
Bud Neck ◽  
Er Membrane

Polarized cells frequently use diffusion barriers to separate plasma membrane domains. It is unknown whether diffusion barriers also compartmentalize intracellular organelles. We used photobleaching techniques to characterize protein diffusion in the yeast endoplasmic reticulum (ER). Although a soluble protein diffused rapidly throughout the ER lumen, diffusion of ER membrane proteins was restricted at the bud neck. Ultrastructural studies and fluorescence microscopy revealed the presence of a ring of smooth ER at the bud neck. This ER domain and the restriction of diffusion for ER membrane proteins through the bud neck depended on septin function. The membrane-associated protein Bud6 localized to the bud neck in a septin-dependent manner and was required to restrict the diffusion of ER membrane proteins. Our results indicate that Bud6 acts downstream of septins to assemble a fence in the ER membrane at the bud neck. Thus, in polarized yeast cells, diffusion barriers compartmentalize the ER and the plasma membrane along parallel lines.

Sign in / Sign up

Export Citation Format

Share Document