Two configurations of a channel-forming membrane protein

Unwin, P.N.T.; Ennis, Peter D.

doi:10.1038/307609a0

Cited by 356 publications

(188 citation statements)

References 22 publications

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“…Unstained, frozen-hydrated microtubules [54] have a uniform mean diameter which corresponds closely to X-ray fiber diffraction data. Diffraction intensities along F-actin filament [55] and gap junction membrane [56] layer lines also closely agree with those from X-ray diffraction. The remarkable agreement between dimensions of aqueous samples measured by X-ray diffraction and frozen-hydrated specimens measured by electron microscopy is somewhat surprising since water expands 2-3% upon freezing to the vitreous state.…”

Section: Preservation Of Biological Samples In the Frozen-hydrated Statesupporting

confidence: 70%

Magnification calibration and the determination of spherical virus diameters using cryo-microscopy

Olson

Baker

1989

Ultramicroscopy

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The diameters of several frozen-hydrated, spherical viruses were determined using polyoma virus as either an external or an internal calibration standard. The methods described provide a reproducible and accurate way to calibrate microscope magnification. The measured diameters are in excellent agreement with respective measurements previously reported for aqueous samples at room temperature using X-ray diffraction methods. These results indicate that the native morphology and dimensions of biological macromolecules are better preserved in frozen-hydrated samples when compared with more conventional electron microscopy techniques such as negative-staining, metal shadowing or thin-sectioning.

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Section: Preservation Of Biological Samples In the Frozen-hydrated Statesupporting

confidence: 70%

Magnification calibration and the determination of spherical virus diameters using cryo-microscopy

Olson

Baker

1989

Ultramicroscopy

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“…The fine structure of the cell-to-cell channel has been well studied and defined as a gap junction which consists of six identical, rod-shaped protein subunits [59]. This transmembrane channel permits free exchange of ions and small molecules between contacting cells [53].…”

mentioning

confidence: 99%

Modulation of cell communication and carcinogenesis.

Kanno

1985

Jpn.J.Physiol

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In many types of tissue and culture cells, the interiors of adjacent cells communicate with each other through cell-to-cell channels. The fine structure of the cell-to-cell channel has been well studied and defined as a gap junction which consists of six identical, rod-shaped protein subunits [59]. This transmembrane channel permits free exchange of ions and small molecules between contacting cells [53]. This type of interaction between cells has been called "gap junctionalThis communication is readily proved by three different methods : electrophysiological, fluorescent dye transfer and metabolic cooperation methods [33].Cell communication has been thought to be regulated by the concentration of intracellular Ca2+ [45,46] and CAMP [17]. Calcium ion produces graded changes in cell communication [47]. cAMP modulates cell communication by stimulating the de novo synthesis of gap junctional protein [17].Since extensive reviews on the general properties of the gap junction and its physiological role have appeared in recent years [33,34], this short review will deal with a limited topic, namely, recent studies on the physiological role of gap junctional cell communication in the phenotypic manifestation of cancer. I. CELL COMMUNICATION IN CANCER CELLSInvestigation of cell communication in cancer cells was first made in rat liver tumors including primary, Morris and Novikoff hepatomas by electrophysiological methods [35]. Subsequently, similar studies were performed in transplanted rat and hamster thyroid tumors [24] and human stomach carcinoma [28]. These earlier studies showed a lack or a decrease of cell communication between contacting cancer cells, indicating the predominance of communication-incompetent cells in malignant tumors. A solid tumor, which was developed by transplantation of MH 134 cells into the subcutaneous space of C3H/He mice showed a decreased level of communication as revealed by electrical coupling. The decrease of cell communication appeared to correlate with the characteristics of metastasis in the case of MH 134 cells [23]. In benign tumors, such as human follicular adenoma, human diffuse toxic goiter and nontoxic nodular goiter, con-

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“…The general higher-order structure of gap junction channels was first revealed by electron cryomicroscopy and image analysis of two-dimensional crystals at 19 Å resolution [4]. Twodimensional projection maps at 7 Å resolution revealed superimposed α-helices that could only arise if the connexons are rotationally staggered by 30° around the 6-fold symmetry axis [5] ( Figure 1a).…”

Section: The Connexon Contains a Ring Of 24 α-Helicesmentioning

confidence: 99%

“…The primary tools for structure analysis of gap junction channels include electron microscopy and image analysis [4][5][6][7][8][9], X-ray diffraction [10][11][12], nuclear magnetic resonance (NMR) spectroscopy [13][14][15] and atomic force microscopy (AFM) [16][17][18]. Mutagenic, biochemical and electrophysiological approaches have also been used to elucidate the structure-function relationships of gap junction channels.…”

Section: Introductionmentioning

confidence: 99%

Gap junction channel structure in the early 21st century: facts and fantasies

Yeager

Harris

2007

Current Opinion in Cell Biology

133

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Gap junction channels connect the cytoplasms of adjacent cells through the end-to-end docking of single-membrane structures called connexons, formed by a ring of six connexin monomers. Each monomer contains 4 transmembrane α-helices, for a total of 24 α-helices in a connexon. The fundamental structure of the connexon pore is probably similar in unpaired connexons and junctional channels, and for channels formed by different connexin isoforms. Nevertheless, variability in results from structurally-focused mutagenesis and electrophysiological studies raise uncertainty about the specific assignments of the transmembrane helices. Mapping of human mutations onto a suggested C α model predicts that mutations that disrupt helix-helix packing impair channel function. An experimentally determined structure at atomic resolution will be essential to confirm and resolve these concepts.

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Two configurations of a channel-forming membrane protein

Cited by 356 publications

References 22 publications

Magnification calibration and the determination of spherical virus diameters using cryo-microscopy

Magnification calibration and the determination of spherical virus diameters using cryo-microscopy

Modulation of cell communication and carcinogenesis.

Gap junction channel structure in the early 21st century: facts and fantasies

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