Distribution of transport proteins over animal cell membranes

Almers, Wolfhard; Stirling, Charles E.

doi:10.1007/bf01870567

Cited by 126 publications

(49 citation statements)

References 144 publications

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“…Another unique characteristic of the RPE is the "reversed polarity" of proteins such as the Na,K-ATPase pump, EMMPRIN, and the adhesion molecule N-CAM at the apical surface, rather than at the basolateral surface where these proteins are found in other epithelia (6 -9). However, the RPE shares many of the com-mon characteristics of other transporting epithelia such as the presence of antioxidative enzymes, amino peptidase (7), and the glucose transporter (10,11) in their apical microvilli.…”

Section: Molecular and Cellular Proteomics 3:1119 -1127 2004mentioning

confidence: 99%

Proteomic Characterization of Isolated Retinal Pigment Epithelium Microvilli

Bonilha

Bhattacharya

West

et al. 2004

Molecular & Cellular Proteomics

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Polarized epithelial cells are characterized by displaying compartmentalized functions associated with differential distribution of transporters, structural proteins, and signaling molecules on their apical and basolateral surfaces. Their apical surfaces frequently elaborate microvilli, which vary in structure according to the specific type and function of each epithelium. The molecular basis of this heterogeneity is poorly understood. However, differences in function will undoubtedly be reflected in the specific molecular composition of the apical surface in each epithelial subtype. We have exploited a method for isolating microvilli from the mouse eye using wheat germ agglutinin (WGA)-agarose beads to begin to understand the specific molecular composition of apical microvilli of the retinal pigment epithelium (RPE) and expand our knowledge of the potential function of this interface. Initially, apical RPE plasma membranes bound to WGA beads were processed for morphological analysis using known apical and basolateral surface markers. The protein composition of the apical microvilli was then established using proteomic analysis. Over 200 proteins were identified, including a number of proteins previously known to be localized to RPE microvilli, as well as others not known to be present at this surface. Localization of novel proteins identified with proteomics was confirmed by immunohistochemistry in both mouse and rat eye tissue. The data generated provides new information on the protein composition of the RPE apical microvilli. The isolation technique used should be amenable for isolating microvilli in other epithelia as well, allowing new insights into additional functions of this important epithelial compartment. Molecular & Cellular Proteomics 3:1119 -1127, 2004.Epithelial cells are characterized by the asymmetric distribution of proteins and lipids in their plasma membrane: a basic feature referred to as polarity. The functional polarity of epithelial cells is dependent on the asymmetric distribution of specific enzymes, signaling molecules, and transport proteins between their apical and basolateral surface membranes (1). The apical surface of cuboidal and columnar epithelial cells commonly faces a luminal cavity and is characterized by the presence of numerous surface membrane elaborations referred to as microvilli. Microvilli greatly increase the apical surface area and, consequently, the number of transport and signaling proteins it contains, thereby enhancing the epithelial functional capacity. Absorptive epithelia such as kidney and intestine have their apical surface decorated with highly organized apical microvilli of uniform length and width. More dynamic and less organized structures are present in the epithelial cells of the placenta and the retinal pigment epithelium (RPE), 1 which perform endocytosis and phagocytosis, respectively. The basis of this morphological heterogeneity is poorly understood and is likely to be related to the specialized function and specific molecular composition of the ...

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Section: Molecular and Cellular Proteomics 3:1119 -1127 2004mentioning

confidence: 99%

Proteomic Characterization of Isolated Retinal Pigment Epithelium Microvilli

Bonilha

Bhattacharya

West

et al. 2004

Molecular & Cellular Proteomics

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“…Since one of the large-patch experiments seemed to isolate a region of pure A-current, a minimum diameter of such a raft would be about 3 ,tm assuming that the membrane under the pipette was not extensively drawn into the tip. There is good evidence for discrete channel localization from a variety of preparations (see review by Almers & Stirling, 1984). Possible mechanisms by which channel localization may occur have been discussed by Fraser & Poo (1982) in relation to the acetylcholine receptor.…”

Section: Microscopic A-current Measurementsmentioning

confidence: 99%

Selectivity and patch measurements of A‐current channels in Helix aspersa neurones.

Taylor

1987

The Journal of Physiology

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SUMMARY1. The ionic selectivity ofA-current K+ channels has been measured in single Helix aspersa neurones by recording the reversal potential shift in test solutions containing various monovalent cations.2. The A-current channel is permeable to Tl+, K+, Rb+, NH4+ and Cs+. The channels may also be sparingly permeable to Na+ and Li+. Organic cations have an apparent small permeability as judged from their reversal potentials, but this may be an artifact of K+ accumulation.3. A large patch electrode (3 ,m tip) isolated a region that appeared to contain only A-current channels. This may indicate that A-current channels are found in the membrane as rafts of at least 3 gtm in diameter.4. The single-channel conductance calculated from single-channel current steps was 14 pS.

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“…This variation 1. Abbreviations used in this paper: dil C14,1,3,3',3' tetramethylindocarbocyanine; is not an artifact of the measuring system. Our data strongly indicate that fibroblast surface membranes consist of proteinrich domains ~1 tun in diameter, embedded in a relatively protein-poor lipid continuum.…”

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confidence: 99%

Micrometer-scale domains in fibroblast plasma membranes.

Yechiel¹,

Edidin²

1987

The Journal of Cell Biology

230

151

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Abstract. We have used the technique of fluorescence photobleaching recovery to measure the lateral diffusion coefficients and the mobile fractions of a fluorescent lipid probe, 1-acyl-2-(12-[(7-nitro-2-1,3-benzoxadiazol-4-yl)aminododecanoyl]) phosphatidylcholine (NBD-PC), and of labeled membrane proteins of human fibroblasts. Values for mobile fractions decrease monotonically with increasing size of the laser spot used for the measurements, over a range of 0.35-5.0 ~tm. Values for NBD-PC diffusion coefficients increase in part of this range to reach a plateau at larger laser spots. This variation is not an artifact of the measuring system, since the effects are not seen if diffusion of the probe is measured in liposomes. We also find that the distribution of diffusion coefficients measured with small laser spots is heterogeneous indicating that these small spots can sample different regions of the membrane. These regions appear to differ in protein concentration. Our data strongly indicate that fibroblast surface membranes consist of protein-rich domains ,,ol grn in diameter, embedded in a relatively protein-poor lipid continuum. These features appear in photographs of labeled cell surfaces illuminated by the expanded laser beam.T I-IE organization of membrane lipids and proteins, and the role of this organization in membrane function, are major topics in modem biology. The commonly quoted model of membrane structure posits a random distribution of membrane molecules (16), but does not rule out the possibility that membrane lipids and proteins may be organized into domains whose protein and lipid composition differ from the bulk of the membrane. Such domains, which measure on the scale of tens of micrometers, are found in the plasma membranes of many tissue cells, notably in functionally polarized cells (1,4,17). Evidence for smaller domains in less specialized surface membranes comes from experiments showing complex behavior of lipid labels in cell membranes different from the behavior of these probes in simple liposome membranes (9)(10)(11)(18)(19)(20). Such experiments often require determination of multiple values (e.g., of fluorescence lifetime) from single experimental curves, or depend upon the use of several different lipids or lipid analogs.We now show that the lateral diffusion of a single species of lipid label, 1-acyl-2-(12-[(7-nitro-2-1, 3-benzoxadiazol-4yl) aminododecanoyl]phosphatidylcholine (NBD-PC), l gives strong evidence for the existence of lipid domains, in fibroblast plasma membranes. The diffusion coefficient and the mobile fraction of a single fluorescent lipid probe, NBD-PC, and of labeled membrane proteins, vary with the size of the laser spot used to probe the labeled surface. This variation 1. Abbreviations used in this paper: dil C14,1,3,3',3' tetramethylindocarbocyanine; is not an artifact of the measuring system. Our data strongly indicate that fibroblast surface membranes consist of proteinrich domains ~1 tun in diameter, embedded in a relatively protein-poor lipid continuum. Mat...

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Distribution of transport proteins over animal cell membranes

Cited by 126 publications

References 144 publications

Proteomic Characterization of Isolated Retinal Pigment Epithelium Microvilli

Proteomic Characterization of Isolated Retinal Pigment Epithelium Microvilli

Selectivity and patch measurements of A‐current channels in Helix aspersa neurones.

Micrometer-scale domains in fibroblast plasma membranes.

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