scholarly journals Tales of tails in transporters

Open Biology ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 190083 ◽  
Author(s):  
Emmanuel Mikros ◽  
George Diallinas
Keyword(s):  
Plasma Membrane ◽  
Substrate Recognition ◽  
Expression Stability ◽  
Functional Importance ◽  
Substrate Specificities ◽  
Transport Dynamics ◽  
Transmembrane Segments ◽  
Extracellular Loops ◽  
Cell Nutrition ◽  
Fine Structures

Cell nutrition, detoxification, signalling, homeostasis and response to drugs, processes related to cell growth, differentiation and survival are all mediated by plasma membrane (PM) proteins called transporters. Despite their distinct fine structures, mechanism of function, energetic requirements, kinetics and substrate specificities, all transporters are characterized by a main hydrophobic body embedded in the PM as a series of tightly packed, often intertwined, α-helices that traverse the lipid bilayer in a zigzag mode, connected with intracellular or extracellular loops and hydrophilic N- and C-termini. Whereas longstanding genetic, biochemical and biophysical evidence suggests that specific transmembrane segments, and also their connecting loops, are responsible for substrate recognition and transport dynamics, emerging evidence also reveals the functional importance of transporter N- and C-termini, in respect to transport catalysis, substrate specificity, subcellular expression, stability and signalling. This review highlights selected prototypic examples of transporters in which their termini play important roles in their functioning.

Membrane microdomains: lessons from microscopy

1995 ◽  
Vol 53 ◽  
pp. 776-777
Author(s):  
J.M. Robinson ◽  
J.M Oliver
Keyword(s):  
Spatial Distribution ◽  
Plasma Membrane ◽  
Epithelial Cells ◽  
Plasma Membranes ◽  
Cell Types ◽  
Imaging Modalities ◽  
Membrane Microdomains ◽  
Membrane Domains ◽  
Lateral Heterogeneity ◽  
Functional Importance

Specialized regions of plasma membranes displaying lateral heterogeneity are the focus of this Symposium. Specialized membrane domains are known for certain cell types such as differentiated epithelial cells where lateral heterogeneity in lipids and proteins exists between the apical and basolateral portions of the plasma membrane. Lateral heterogeneity and the presence of microdomains in membranes that are uniform in appearance have been more difficult to establish. Nonetheless a number of studies have provided evidence for membrane microdomains and indicated a functional importance for these structures.This symposium will focus on the use of various imaging modalities and related approaches to define membrane microdomains in a number of cell types. The importance of existing as well as emerging imaging technologies for use in the elucidation of membrane microdomains will be highlighted. The organization of membrane microdomains in terms of dimensions and spatial distribution is of considerable interest and will be addressed in this Symposium.

scholarly journals Functional Role of Charged Residues in the Transmembrane Segments of the Yeast Plasma Membrane H+-ATPase

2000 ◽  
Vol 275 (21) ◽  
pp. 15709-15716 ◽  
Author(s):  
Valery V. Petrov ◽  
Kristine P. Padmanabha ◽  
Robert K. Nakamoto ◽  
Kenneth E. Allen ◽  
Carolyn W. Slayman
Keyword(s):  
Plasma Membrane ◽  
Functional Role ◽  
Yeast Plasma Membrane ◽  
Transmembrane Segments ◽  
Charged Residues

Cloning, characterization, and gene organization of K-Cl cotransporter from pig and human kidney and C. elegans

1998 ◽  
Vol 275 (4) ◽  
pp. F550-F564 ◽  
Author(s):  
Eli J. Holtzman ◽  
Sumit Kumar ◽  
Carol A. Faaland ◽  
Fern Warner ◽  
Paul J. Logue ◽  
...  
Keyword(s):  
Amino Acids ◽  
Human Kidney ◽  
Gene Organization ◽  
Kidney Cells ◽  
Hek 293 ◽  
Human Embryonic Kidney Cells ◽  
C Elegans ◽  
Transmembrane Segments ◽  
Extracellular Loops ◽  
Stimulation Of

We isolated and characterized the cDNAs for the human, pig, and Caenorhabditis elegansK-Cl cotransporters. The pig and human homologs are 94% identical and contain 1,085 and 1,086 amino acids, respectively. The deduced protein of the C. elegans K-Cl cotransporter clone (CE-KCC1) contains 1,003 amino acids. The mammalian K-Cl cotransporters share ∼45% similarity with CE-KCC1. Hydropathy analyses of the three clones indicate typical KCC topology patterns with 12 transmembrane segments, large extracellular loops between transmembrane domains 5 and 6 (unique to KCC), and large COOH-terminal domains. Human KCC1 is widely expressed among various tissues. This KCC1 gene spans 23 kb and is organized in 24 exons, whereas the CE-KCC1 gene spans 3.5 kb and contains 10 exons. Transiently and stably transfected human embryonic kidney cells (HEK-293) expressing the human, pig, and C. elegans K-Cl cotransporter fulfilled two (pig) or five (human and C. elegans) criteria for increased expression of the K-Cl cotransporter. The criteria employed were basal K-Cl cotransport; stimulation of cotransport by swelling, N-ethylmaleimide, staurosporine, and reduced cell Mg concentration; and secondary stimulation of Na-K-Cl cotransport.

Plasma-membrane electrical responses to salt and osmotic gradients contradict radiotracer kinetics, and reveal Na+-transport dynamics in rice (Oryza sativa L.)

Planta ◽  
2018 ◽  
Vol 249 (4) ◽  
pp. 1037-1051 ◽  
Author(s):  
Ahmed M. Hamam ◽  
Devrim Coskun ◽  
Dev T. Britto ◽  
Darren Plett ◽  
Herbert J. Kronzucker
Keyword(s):  
Oryza Sativa ◽  
Plasma Membrane ◽  
Oryza Sativa L ◽  
Na Transport ◽  
Transport Dynamics ◽  
Electrical Responses

scholarly journals Palmitoylated Cysteines in Chikungunya Virus nsP1 Are Critical for Targeting to Cholesterol-Rich Plasma Membrane Microdomains with Functional Consequences for Viral Genome Replication

2020 ◽  
Vol 94 (10) ◽  
Author(s):  
William Bakhache ◽  
Aymeric Neyret ◽  
Eric Bernard ◽  
Andres Merits ◽  
Laurence Briant
Keyword(s):  
Plasma Membrane ◽  
Lipid Bilayers ◽  
Functional Role ◽  
Membrane Microdomains ◽  
Genome Replication ◽  
Functional Importance ◽  
Late Endosomes ◽  
Plasma Membrane Microdomains ◽  
Insight Into

ABSTRACT In mammalian cells, alphavirus replication complexes are anchored to the plasma membrane. This interaction with lipid bilayers is mediated through the viral methyl/guanylyltransferase nsP1 and reinforced by palmitoylation of cysteine residue(s) in the C-terminal region of this protein. Lipid content of membranes supporting nsP1 anchoring remains poorly studied. Here, we explore the membrane binding capacity of nsP1 with regard to cholesterol. Using the medically important chikungunya virus (CHIKV) as a model, we report that nsP1 cosegregates with cholesterol-rich detergent-resistant membrane microdomains (DRMs), also called lipid rafts. In search for the critical factor for cholesterol partitioning, we identify nsP1 palmitoylated cysteines as major players in this process. In cells infected with CHIKV or transfected with CHIKV trans-replicase plasmids, nsP1, together with the other nonstructural proteins, are detected in DRMs. While the functional importance of CHIKV nsP1 preference for cholesterol-rich membrane domains remains to be determined, we observed that U18666A- and imipramine-induced sequestration of cholesterol in late endosomes redirected nsP1 to these compartments and simultaneously dramatically decreased CHIKV genome replication. A parallel study of Sindbis virus (SINV) revealed that nsP1 from this divergent alphavirus displays a low affinity for cholesterol and only moderately segregates with DRMs. Behaviors of CHIKV and SINV with regard to cholesterol, therefore, match with the previously reported differences in the requirement for nsP1 palmitoylation, which is dispensable for SINV but strictly required for CHIKV replication. Altogether, this study highlights the functional importance of nsP1 segregation with DRMs and provides new insight into the functional role of nsP1 palmitoylated cysteines during alphavirus replication. IMPORTANCE Functional alphavirus replication complexes are anchored to the host cell membranes through the interaction of nsP1 with the lipid bilayers. In this work, we investigate the importance of cholesterol for such an association. We show that nsP1 has affinity for cholesterol-rich membrane microdomains formed at the plasma membrane and identify conserved palmitoylated cysteine(s) in nsP1 as the key determinant for cholesterol affinity. We demonstrate that drug-induced cholesterol sequestration in late endosomes not only redirects nsP1 to this compartment but also dramatically decreases genome replication, suggesting the functional importance of nsP1 targeting to cholesterol-rich plasma membrane microdomains. Finally, we show evidence that nsP1 from chikungunya and Sindbis viruses displays different sensitivity to cholesterol sequestering agents that parallel with their difference in the requirement for nsP1 palmitoylation for replication. This research, therefore, gives new insight into the functional role of palmitoylated cysteines in nsP1 for the assembly of functional alphavirus replication complexes in their mammalian host.

scholarly journals Proline residues in transmembrane segment IV are critical for activity, expression and targeting of the Na+/H+ exchanger isoform 1

2004 ◽  
Vol 379 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Emily R. SLEPKOV ◽  
Signy CHOW ◽  
M. Joanne LEMIEUX ◽  
Larry FLIEGEL
Keyword(s):  
Plasma Membrane ◽  
Membrane Protein ◽  
Mammalian Cells ◽  
Integral Membrane Protein ◽  
Amide Hydrogen ◽  
Wild Type ◽  
Transmembrane Segment ◽  
Mutant Proteins ◽  
Transmembrane Segments ◽  
Induced Changes

NHE1 (Na+/H+ exchanger isoform 1) is a ubiquitously expressed integral membrane protein that regulates intracellular pH in mammalian cells. Proline residues within transmembrane segments have unusual properties, acting as helix breakers and increasing flexibility of membrane segments, since they lack an amide hydrogen. We examined the importance of three conserved proline residues in TM IV (transmembrane segment IV) of NHE1. Pro167 and Pro168 were mutated to Gly, Ala or Cys, and Pro178 was mutated to Ala. Pro168 and Pro178 mutant proteins were expressed at levels similar to wild-type NHE1 and were targeted to the plasma membrane. However, the mutants P167G (Pro167→Gly), P167A and P167C were expressed at lower levels compared with wild-type NHE1, and a significant portion of P167G and P167C were retained intracellularly, possibly indicating induced changes in the structure of TM IV. P167G, P167C, P168A and P168C mutations abolished NHE activity, and P167A and P168G mutations caused markedly decreased activity. In contrast, the activity of the P178A mutant was not significantly different from that of wild-type NHE1. The results indicate that both Pro167 and Pro168 in TM IV of NHE1 are required for normal NHE activity. In addition, mutation of Pro167 affects the expression and membrane targeting of the exchanger. Thus both Pro167 and Pro168 are strictly required for NHE function and may play critical roles in the structure of TM IV of the NHE.

scholarly journals Evidence for a Salt Bridge between Transmembrane Segments 5 and 6 of the Yeast Plasma-membrane H+-ATPase

1998 ◽  
Vol 273 (51) ◽  
pp. 34328-34334 ◽  
Author(s):  
Soma Sen Gupta ◽  
Natalie D. DeWitt ◽  
Kenneth E. Allen ◽  
Carolyn W. Slayman
Keyword(s):  
Plasma Membrane ◽  
Salt Bridge ◽  
Yeast Plasma Membrane ◽  
Transmembrane Segments

scholarly journals Substrate specificities of mouse heparan sulphate glucosaminyl 6-O-sulphotransferases

2003 ◽  
Vol 372 (2) ◽  
pp. 371-380 ◽  
Author(s):  
Emanuel SMEDS ◽  
Hiroko HABUCHI ◽  
Anh-Tri DO ◽  
Eva HJERTSON ◽  
Helena GRUNDBERG ◽  
...  
Keyword(s):  
Growth Factors ◽  
Glucuronic Acid ◽  
Heparan Sulphate ◽  
Sulphate Group ◽  
Functional Importance ◽  
Cellular Functions ◽  
Recombinant Enzymes ◽  
Substrate Specificities ◽  
Iduronic Acid ◽  
Target Sequences

Glycosaminoglycan heparan sulphate interacts with a variety of proteins, such as growth factors, cytokines, enzymes and inhibitors and, thus, influences cellular functions, including adhesion, motility, differentiation and morphogenesis. The interactions generally involve saccharide domains in heparan sulphate chains, with precisely located O-sulphate groups. The 6-O-sulphate groups on glucosamine units, supposed to be involved in various interactions of functional importance, occur in different structural contexts. Three isoforms of the glucosaminyl 6-O-sulphotransferase (6-OST) have been cloned and characterized [H. Habuchi, M. Tanaka, O. Habuchi, K. Yoshida, H. Suzuki, K. Ban and K. Kimata (2000) J. Biol. Chem. 275, 2859–2868]. We have studied the substrate specificities of the recombinant enzymes using various O-desulphated poly- and oligo-saccharides as substrates, and using adenosine 3′-phosphate 5′-phospho[35S]sulphate as sulphate donor. All three enzymes catalyse 6-O-sulphation of both -GlcA-GlcNS- and -IdoA-GlcNS- (where GlcA represents d-glucuronic acid, NS the N-sulphate group and IdoA the l-iduronic acid) sequences, with preference for IdoA-containing targets, with or without 2-O-sulphate substituents. 6-OST1 showed relatively higher activity towards target sequences lacking 2-O-sulphate, e.g. the -GlcA-GlcNS- disaccharide unit. Sulphation of such non-O-sulphated acceptor sequences was generally favoured at low acceptor polysaccharide concentrations. Experiments using partially O-desulphated antithrombin-binding oligosaccharide as the acceptor revealed 6-O-sulphation of N-acetylated as well as 3-O-sulphated glucosamine residues with each of the three 6-OSTs. We conclude that the three 6-OSTs have qualitatively similar substrate specificities, with minor differences in target preference.

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