Removal of phospho-head groups of membrane lipids immobilizes voltage sensors of K+ channels

In higher eukaryotes, glucosylceramide is the simplest member and precursor of a fascinating class of membrane lipids, the glycosphingolipids. These lipids display an astounding variation in their carbohydrate head groups, suggesting that glycosphingolipids serve specialized functions in recognition processes. It is now realized that they are organized in signalling domains on the cell surface. They are of vital importance as, in their absence, embryonal development is inhibited at an early stage. Remarkably, individual cells can live without glycolipids, perhaps because their survival does not depend on glycosphingolipid–mediated signalling mechanisms. Still, these cells suffer from defects in intracellular membrane transport. Various membrane proteins do not reach their intracellular destination, and, indeed, some intracellular organelles do not properly differentiate to their mature stage. The fact that glycosphingolipids are required for cellular differentiation suggests that there are human diseases resulting from defects in glycosphingolipid synthesis. In addition, the same cellular differentiation processes may be affected by defects in the degradation of glycosphingolipids. At the cellular level, the pathology of glycosphingolipid storage diseases is not completely understood. Cell biological studies on the intracellular fate and function of glycosphingolipids may open new ways to understand and defeat not only lipid storage diseases, but perhaps other diseases that have not been connected to glycosphingolipids so far.

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A laboratory experiment of intact polar lipid degradation in sandy sediments

Biogeosciences ◽

10.5194/bg-8-2547-2011 ◽

2011 ◽

Vol 8 (9) ◽

pp. 2547-2560 ◽

Cited By ~ 62

Author(s):

J. Logemann ◽

J. Graue ◽

J. Köster ◽

B. Engelen ◽

J. Rullkötter ◽

...

Keyword(s):

North Sea ◽

Membrane Lipids ◽

Intact Cells ◽

The North ◽

Head Groups ◽

Acyl Lipids ◽

The North Sea ◽

Intact Polar Lipids ◽

A Minor ◽

Sandy Sediments

Abstract. Intact polar lipids (IPLs) are considered biomarkers for living biomass. Their degradation in marine sediments, however, is poorly understood and complicates interpretation of their occurrence in geological samples. To investigate the turnover of IPLs, a degradation experiment with anoxic sandy sediments from the North Sea was conducted. Intact cells of two organisms that do not naturally occur in North Sea sediments were chosen as IPL sources: (i) Saccharomyces cerevisiae, representative for ester-bound acyl lipids that also occur in Bacteria, and (ii) the archaeon Haloferax volcanii, representative for ether-bound isoprenoid lipids. Surprisingly, IPLs with phosphoester-bound head groups showed approximately the same degradation rate as IPLs with glycosidic head groups. Furthermore, the results indicate a relatively fast degradation of S. cerevisiae IPLs with ester-bound moieties (analogs of bacterial membrane lipids) and no significant degradation of archaeal IPLs with ether-bound moieties. Pore water and 16S rRNA-based DGGE analysis showed only a minor influence of the IPL source on microbial metabolism and community profiles. Due to our results, the IPL-based quantification of Archaea and Bacteria should be interpreted with caution.

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The Cell Membrane of Sulfolobus spp.—Homeoviscous Adaption and Biotechnological Applications

International Journal of Molecular Sciences ◽

10.3390/ijms21113935 ◽

2020 ◽

Vol 21 (11) ◽

pp. 3935 ◽

Cited By ~ 1

Author(s):

Kerstin Rastädter ◽

David J. Wurm ◽

Oliver Spadiut ◽

Julian Quehenberger

Keyword(s):

Cell Membrane ◽

Environmental Changes ◽

Specific Growth ◽

Membrane Lipids ◽

Environmental Parameters ◽

Coping Mechanism ◽

Biotechnological Applications ◽

Head Groups ◽

Tetraether Lipids ◽

Archaeal Lipids

The microbial cell membrane is affected by physicochemical parameters, such as temperature and pH, but also by the specific growth rate of the host organism. Homeoviscous adaption describes the process of maintaining membrane fluidity and permeability throughout these environmental changes. Archaea, and thereby, Sulfolobus spp. exhibit a unique lipid composition of ether lipids, which are altered in regard to the ratio of diether to tetraether lipids, number of cyclopentane rings and type of head groups, as a coping mechanism against environmental changes. The main biotechnological application of the membrane lipids of Sulfolobus spp. are so called archaeosomes. Archaeosomes are liposomes which are fully or partly generated from archaeal lipids and harbor the potential to be used as drug delivery systems for vaccines, proteins, peptides and nucleic acids. This review summarizes the influence of environmental parameters on the cell membrane of Sulfolobus spp. and the biotechnological applications of their membrane lipids.

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A laboratory experiment of intact polar lipid degradation in sandy sediments

Biogeosciences Discussions ◽

10.5194/bgd-8-3289-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 3289-3321 ◽

Cited By ~ 7

Author(s):

J. Logemann ◽

J. Graue ◽

J. Köster ◽

B. Engelen ◽

J. Rullkötter ◽

...

Keyword(s):

North Sea ◽

Membrane Lipids ◽

Intact Cells ◽

The North ◽

Head Groups ◽

Acyl Lipids ◽

The North Sea ◽

Intact Polar Lipids ◽

A Minor ◽

Sandy Sediments

Abstract. Intact polar lipids (IPLs) are considered biomarkers for living biomass. Their degradation in marine sediments, however, is poorly understood and complicates interpretation of their occurrence in geological samples. To investigate the turnover of IPLs, a degradation experiment with anoxic sandy sediments from the North Sea was conducted. Intact cells of two organisms that do not naturally occur in North Sea sediments were chosen as IPL sources: (i) Saccharomyces cerevisiae, representative for ester-bound acyl lipids that also occur in Bacteria, and (ii) the archaeon Haloferax volcanii, representative for ether-bound isoprenoid lipids. Surprisingly, IPLs with phosphoester-bound head groups showed approximately the same degradation rate as IPLs with glycosidic head groups. Furthermore, the results indicate a relatively fast degradation of S. cerevisiae IPLs with ester-bound moieties (analogs of bacterial membrane lipids) and no significant degradation of archaeal IPLs with ether-bound moieties. Pore water and 16S rRNA-based DGGE analysis showed only a minor influence of the IPL source on microbial metabolism and community profiles. Due to our results, the IPL-based quantification of Archaea and Bacteria should be interpreted with caution.

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Constitutive Activation of the Shaker Kv Channel

The Journal of General Physiology ◽

10.1085/jgp.200308905 ◽

2003 ◽

Vol 122 (5) ◽

pp. 541-556 ◽

Cited By ~ 60

Author(s):

Manana Sukhareva ◽

David H. Hackos ◽

Kenton J. Swartz

Keyword(s):

Single Channel ◽

Membrane Depolarization ◽

Ion Conduction ◽

K Channels ◽

Voltage Sensors ◽

Kv Channel ◽

Kv Channels ◽

Activation Gate ◽

Sensor Activation ◽

Primary Activation

In different types of K+ channels the primary activation gate is thought to reside near the intracellular entrance to the ion conduction pore. In the Shaker Kv channel the gate is closed at negative membrane voltages, but can be opened with membrane depolarization. In a previous study of the S6 activation gate in Shaker (Hackos, D.H., T.H. Chang, and K.J. Swartz. 2002. J. Gen. Physiol. 119:521–532.), we found that mutation of Pro 475 to Asp results in a channel that displays a large macroscopic conductance at negative membrane voltages, with only small increases in conductance with membrane depolarization. In the present study we explore the mechanism underlying this constitutively conducting phenotype using both macroscopic and single-channel recordings, and probes that interact with the voltage sensors or the intracellular entrance to the ion conduction pore. Our results suggest that constitutive conduction results from a dramatic perturbation of the closed-open equilibrium, enabling opening of the activation gate without voltage-sensor activation. This mechanism is discussed in the context of allosteric models for activation of Kv channels and what is known about the structure of this critical region in K+ channels.

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A Gastropod Toxin Selectively Slows Early Transitions in the Shaker K Channel's Activation Pathway

The Journal of General Physiology ◽

10.1085/jgp.200409047 ◽

2004 ◽

Vol 123 (6) ◽

pp. 685-696 ◽

Cited By ~ 15

Author(s):

Jon T. Sack ◽

Richard W. Aldrich ◽

William F. Gilly

Keyword(s):

Single Channel ◽

K Channel ◽

Channel Activity ◽

Gating Currents ◽

K Channels ◽

Voltage Sensors ◽

Essentially Normal ◽

Channel Opening ◽

Single Channel Activity ◽

Kinetics Of

A toxin from a marine gastropod's defensive mucus, a disulfide-linked dimer of 6-bromo-2-mercaptotryptamine (BrMT), was found to inhibit voltage-gated potassium channels by a novel mechanism. Voltage-clamp experiments with Shaker K channels reveal that externally applied BrMT slows channel opening but not closing. BrMT slows K channel activation in a graded fashion: channels activate progressively slower as the concentration of BrMT is increased. Analysis of single-channel activity indicates that once a channel opens, the unitary conductance and bursting behavior are essentially normal in BrMT. Paralleling its effects against channel opening, BrMT greatly slows the kinetics of ON, but not OFF, gating currents. BrMT was found to slow early activation transitions but not the final opening transition of the Shaker ILT mutant, and can be used to pharmacologically distinguish early from late gating steps. This novel toxin thus inhibits activation of Shaker K channels by specifically slowing early movement of their voltage sensors, thereby hindering channel opening. A model of BrMT action is developed that suggests BrMT rapidly binds to and stabilizes resting channel conformations.

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Intact Polar and Core Glycerol Dibiphytanyl Glycerol Tetraether Lipids of Group I.1a and I.1b Thaumarchaeota in Soil

Applied and Environmental Microbiology ◽

10.1128/aem.01681-12 ◽

2012 ◽

Vol 78 (19) ◽

pp. 6866-6874 ◽

Cited By ~ 106

Author(s):

Jaap S. Sinninghe Damsté ◽

W. Irene C. Rijpstra ◽

Ellen C. Hopmans ◽

Man-Young Jung ◽

Jong-Geol Kim ◽

...

Keyword(s):

Agricultural Soils ◽

Membrane Lipids ◽

Hydroxyl Group ◽

Head Group ◽

Aquatic Environments ◽

Content Type ◽

Group I ◽

Head Groups ◽

Intact Membrane ◽

Tetraether Lipids

ABSTRACTEcological studies of thaumarchaeota often apply glycerol dibiphytanyl glycerol tetraether (GDGT)-based intact membrane lipids. However, these components have only been characterized for thaumarchaeota from aquatic environments. Thaumarchaeota have been shown to play an important role in the nitrogen cycle in soil as ammonium oxidizers, and GDGTs are common lipids encountered in soil. We report the core and intact polar lipid (IPL) GDGTs produced by three newly available thaumarchaeota isolated from grassland soil in Austria (“Nitrososphaera viennensis,” group I.1b) and enriched from agricultural soils in South Korea (“CandidatusNitrosoarchaeum koreensis” MY1, group I.1a; and “CandidatusNitrososphaera” strain JG1, group I.1b). The soil thaumarchaeota all synthesize crenarchaeol as their major core GDGT, in agreement with the fact that crenarchaeol has also been detected in thaumarchaeota from aquatic environments. The crenarchaeol regioisomer apparently is produced in significant quantities only by soil thaumarchaeota of the I.1b subgroup. In addition, GDGTs with 0 to 4 cyclopentane moieties and GDGTs containing an additional hydroxyl group were detected. The IPL head groups of their membrane lipids comprised mainly monohexose, dihexose, trihexose, phosphohexose, and hexose-phosphohexose moieties. The hexose-phosphohexose head group bound to crenarchaeol occurred in all soil thaumarchaeota, and this IPL is at present the only lipid that is detected in all thaumarchaeota analyzed so far. This specificity and its lability indicate that it is the most suitable biomarker lipid to trace living thaumarchaeota. This study, in combination with previous studies, also suggests that hydroxylated GDGTs occur in the I.1a, but not in the I.1b, subgroup of the thaumarchaeota.

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Coupling between Voltage Sensors and Activation Gate in Voltage-gated K+ Channels

The Journal of General Physiology ◽

10.1085/jgp.20028696 ◽

2002 ◽

Vol 120 (5) ◽

pp. 663-676 ◽

Cited By ~ 227

Author(s):

Zhe Lu ◽

Angela M. Klem ◽

Yajamana Ramu

Keyword(s):

Electrical Signal ◽

K Channel ◽

Coupling Mechanism ◽

Excitable Cells ◽

Voltage Sensing ◽

K Channels ◽

Voltage Sensors ◽

Voltage Gated ◽

Transmembrane Segments ◽

Activation Gate

Current through voltage-gated K+ channels underlies the action potential encoding the electrical signal in excitable cells. The four subunits of a voltage-gated K+ channel each have six transmembrane segments (S1–S6), whereas some other K+ channels, such as eukaryotic inward rectifier K+ channels and the prokaryotic KcsA channel, have only two transmembrane segments (M1 and M2). A voltage-gated K+ channel is formed by an ion-pore module (S5–S6, equivalent to M1–M2) and the surrounding voltage-sensing modules. The S4 segments are the primary voltage sensors while the intracellular activation gate is located near the COOH-terminal end of S6, although the coupling mechanism between them remains unknown. In the present study, we found that two short, complementary sequences in voltage-gated K+ channels are essential for coupling the voltage sensors to the intracellular activation gate. One sequence is the so called S4–S5 linker distal to the voltage-sensing S4, while the other is around the COOH-terminal end of S6, a region containing the actual gate-forming residues.

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