1
|
Roig SR, Cassinelli S, Zeug A, Ponimaskin E, Felipe A. Oligomerization and Spatial Distribution of Kvβ1.1 and Kvβ2.1 Regulatory Subunits. Front Physiol 2022; 13:930769. [PMID: 35784882 PMCID: PMC9247503 DOI: 10.3389/fphys.2022.930769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Accepted: 06/02/2022] [Indexed: 11/13/2022] Open
Abstract
Members of the regulatory Kvβ family modulate the kinetics and traffic of voltage-dependent K+ (Kv) channels. The crystal structure of Kv channels associated with Kvβ peptides suggests a α4/β4 composition. Although Kvβ2 and Kvβ1 form heteromers, evidence supports that only Kvβ2.1 forms tetramers in the absence of α subunits. Therefore, the stoichiometry of the Kvβ oligomers fine-tunes the activity of hetero-oligomeric Kv channel complexes. We demonstrate that Kvβ subtypes form homo- and heterotetramers with similar affinities. The Kvβ1.1/Kvβ2.1 heteromer showed an altered spatial distribution in lipid rafts, recapitulating the Kvβ1.1 pattern. Because Kvβ2 is an active partner of the Kv1.3-TCR complex at the immunological synapse (IS), an association with Kvβ1 would alter this location, shaping the immune response. Differential regulation of Kvβs influences the traffic and architecture of the Kvβ heterotetramer, modulating Kvβ-dependent physiological responses.
Collapse
Affiliation(s)
- Sara R. Roig
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
- Imaging Core Facility, Biozentrum, University of Basel, Basel, Switzerland
| | - Silvia Cassinelli
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
| | - Andre Zeug
- Department of Cellular Neurophysiology, Hannover Medical School, Hannover, Germany
| | - Evgeni Ponimaskin
- Department of Cellular Neurophysiology, Hannover Medical School, Hannover, Germany
| | - Antonio Felipe
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
- *Correspondence: Antonio Felipe,
| |
Collapse
|
2
|
Kacher YG, Karlova MG, Glukhov GS, Zhang H, Zaklyazminskaya EV, Loussouarn G, Sokolova OS. The Integrative Approach to Study of the Structure and Functions of Cardiac Voltage-Dependent Ion Channels. CRYSTALLOGR REP+ 2021. [DOI: 10.1134/s1063774521050072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
3
|
Abstract
Many K(+) channels are oligomeric complexes with intrinsic structural symmetry arising from the homo-tetrameric core of their pore-forming subunits. Allosteric regulation of tetramerically symmetric proteins, whether by intrinsic sensing domains or associated auxiliary subunits, often mirrors the fourfold structural symmetry. Here, through patch-clamp recordings of channel population ensembles and also single channels, we examine regulation of the Ca(2+)- and voltage-activated large conductance Ca(2+)-activated K(+) (BK) channel by associated γ1-subunits. Through expression of differing ratios of γ1:α-subunits, the results reveal an all-or-none functional regulation of BK channels by γ-subunits: channels either exhibit a full gating shift or no shift at all. Furthermore, the γ1-induced shift exhibits a state-dependent labile behavior that recapitulates the fully shifted or unshifted behavior. The γ1-induced shift contrasts markedly to the incremental shifts in BK gating produced by 1-4 β-subunits and adds a new layer of complexity to the mechanisms by which BK channel functional diversity is generated.
Collapse
|
4
|
Yamashita H, Inoue K, Shibata M, Uchihashi T, Sasaki J, Kandori H, Ando T. Role of trimer-trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy. J Struct Biol 2013; 184:2-11. [PMID: 23462099 DOI: 10.1016/j.jsb.2013.02.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Revised: 12/22/2012] [Accepted: 02/12/2013] [Indexed: 10/27/2022]
Abstract
Bacteriorhodopsin (bR) trimers form a two-dimensional hexagonal lattice in the purple membrane of Halobacterium salinarum. However, the physiological significance of forming the lattice has long been elusive. Here, we study this issue by comparing properties of assembled and non-assembled bR trimers using directed mutagenesis, high-speed atomic force microscopy (HS-AFM), optical spectroscopy, and a proton pumping assay. First, we show that the bonds formed between W12 and F135 amino acid residues are responsible for trimer-trimer association that leads to lattice assembly; the lattice is completely disrupted in both W12I and F135I mutants. HS-AFM imaging reveals that both crystallized D96N and non-crystallized D96N/W12I mutants undergo a large conformational change (i.e., outward E-F loop displacement) upon light-activation. However, lattice disruption significantly reduces the rate of conformational change under continuous light illumination. Nevertheless, the quantum yield of M-state formation, measured by low-temperature UV-visible spectroscopy, and proton pumping efficiency are unaffected by lattice disruption. From these results, we conclude that trimer-trimer association plays essential roles in providing bound retinal with an appropriate environment to maintain its full photo-reactivity and in maintaining the natural photo-reaction pathway.
Collapse
Affiliation(s)
- Hayato Yamashita
- Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
| | | | | | | | | | | | | |
Collapse
|
5
|
Sumino A, Sumikama T, Iwamoto M, Dewa T, Oiki S. The open gate structure of the membrane-embedded KcsA potassium channel viewed from the cytoplasmic side. Sci Rep 2013; 3:1063. [PMID: 23323207 PMCID: PMC3545221 DOI: 10.1038/srep01063] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 12/06/2012] [Indexed: 01/24/2023] Open
Abstract
Crystallographic studies of channel proteins have provided insight into the molecular mechanisms of ion channels, even though these structures are obtained in the absence of the membrane and some structural portions have remained unsolved. Here we report the gating structure of the membrane-embedded KcsA potassium channel using atomic force microscopy (AFM). The activation gate of the KcsA channel is located on the intracellular side, and the cytoplasmic domain was truncated to clear the view of this location. Once opened, the individual subunits in the tetramer were resolved with the pore open at the center. Furthermore, AFM was able to capture the previously unsolved bulge helix at the entrance. A molecular dynamics simulation revealed that the bulge helices fluctuated dramatically at the open entryway. This dynamic behavior was observed as vigorous open-channel noise in the single-channel current recordings. The role of the bulge helices in the open gate structure is discussed.
Collapse
Affiliation(s)
- Ayumi Sumino
- Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan
| | | | | | | | | |
Collapse
|
6
|
Abstract
Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.
Collapse
Affiliation(s)
- Olaf Pongs
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universitätsklinikum Hamburg-Eppendorf, Universität Hamburg, Hamburg, Germany.
| | | |
Collapse
|
7
|
Moskalenko AV, Yarova PL, Gordeev SN, Smirnov SV. Single protein molecule mapping with magnetic atomic force microscopy. Biophys J 2010; 98:478-87. [PMID: 20141762 PMCID: PMC2814202 DOI: 10.1016/j.bpj.2009.10.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Revised: 10/06/2009] [Accepted: 10/15/2009] [Indexed: 02/04/2023] Open
Abstract
Understanding the structural organization and distribution of proteins in biological cells is of fundamental importance in biomedical research. The use of conventional fluorescent microscopy for this purpose is limited due to its relatively low spatial resolution compared to the size of a single protein molecule. Atomic force microscopy (AFM), on the other hand, allows one to achieve single-protein resolution by scanning the cell surface using a specialized ligand-coated AFM tip. However, because this method relies on short-range interactions, it is limited to the detection of binding sites that are directly accessible to the AFM tip. We developed a method based on magnetic (long-range) interactions and applied it to investigate the structural organization and distribution of endothelin receptors on the surface of smooth muscle cells. Endothelin receptors were labeled with 50-nm superparamagnetic microbeads and then imaged with magnetic AFM. Considering its high spatial resolution and ability to "see" magnetically labeled proteins at a distance of up to 150 nm, this approach may become an important tool for investigating the dynamics of individual proteins both on the cell membrane and in the submembrane space.
Collapse
Affiliation(s)
| | - Polina L. Yarova
- Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | | | - Sergey V. Smirnov
- Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| |
Collapse
|
8
|
Madden DR, Safferling M. Baculoviral expression of an integral membrane protein for structural studies. Methods Mol Biol 2007; 363:39-57. [PMID: 17272836 DOI: 10.1007/978-1-59745-209-0_3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The baculovirus system has proven successful for the expression of integral membrane proteins for structural studies. A recombinant baculovirus, in which the gene of interest is placed under the control of the late-stage polyhedrin promoter, serves as the starting point for viral expansion and protein expression studies. Using large-scale insect cell culture techniques together with a filter-binding assay for protein function, the conditions of expression, purification, and solubilization can be optimized. As applied to the glutamate receptor ion channel subunit GluR2, this approach yields milligram quantities of pure, active protein, which have been used for single-particle electron microscopic analysis of the receptor structure. Detergent exchange protocols are also discussed, as a prerequisite for two-dimensional crystallization trials.
Collapse
Affiliation(s)
- Dean R Madden
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
| | | |
Collapse
|
9
|
Xicluna J, Lacombe B, Dreyer I, Alcon C, Jeanguenin L, Sentenac H, Thibaud JB, Chérel I. Increased functional diversity of plant K+ channels by preferential heteromerization of the shaker-like subunits AKT2 and KAT2. J Biol Chem 2007; 282:486-94. [PMID: 17085433 DOI: 10.1074/jbc.m607607200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Assembly of plant Shaker subunits as heterotetramers, increasing channel functional diversity, has been reported. Here we focus on a new interaction, between AKT2 and KAT2 subunits. The assembly as AKT2/KAT2 heterotetramers is demonstrated by (i) a strong signal in two-hybrid tests with intracytoplasmic C-terminal regions, (ii) the effect of KAT2 on AKT2 subunit targeting in tobacco cells, (iii) the complete inhibition of AKT2 currents by co-expression with a dominant-negative KAT2 subunit in Xenopus oocytes, and reciprocally, and (iv) the appearance, upon co-expression of wild-type AKT2 and KAT2 subunits, of new channel functional properties that cannot be explained by the co-existence of two kinds of homotetrameric channels. In particular, the instantaneous current, characteristic of AKT2, displayed new functional features when compared with those of AKT2 homotetramers: activation by external acidification (instead of inhibition) and weak inhibition by calcium. Single channel current measurements in oocytes co-expressing AKT2 and KAT2 revealed a strong preference for incorporation of subunits into heteromultimers and a diversity of individual channels. In planta, these new channels, which may undergo specific regulations, are likely to be formed in guard cells and in the phloem, where they could participate in the control of membrane potential and potassium fluxes.
Collapse
Affiliation(s)
- Jérôme Xicluna
- Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, UMR 5004 Agro-Montpellier/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Montpellier II, Place Viala, 34060 Montpellier Cedex 1, France
| | | | | | | | | | | | | | | |
Collapse
|
10
|
Sokolova O. Structure of cation channels, revealed by single particle electron microscopy. FEBS Lett 2004; 564:251-6. [PMID: 15111105 DOI: 10.1016/s0014-5793(04)00254-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Accepted: 02/23/2004] [Indexed: 11/18/2022]
Abstract
A large barrier in the way to obtaining high-resolution structures of eukaryotic ion channels remains the expression and purification of sufficient amounts of channel protein to carry out crystallization trials. In the absence of crystals, the main available source of structural information has been electron microscopy (EM), which is well suited to the visualization of isolated macromolecular complexes and their conformational changes. The recently published EM structures outline native conformations of eukaryotic cation channels that until now have eluded crystallization. According to these results, homo-tetrameric K(+) channels have a distinct two-layer architecture with connectors conjoining the two layers, while the pseudo-tetrameric Ca(2+) or Na(+) channels are more globular and have flexible surface loops, which makes the identification of subunits complicated. Subunits can be identified using atomic structure docking into the EM maps, labeling, or deletion studies.
Collapse
Affiliation(s)
- Olga Sokolova
- Howard Hughes Medical Institute, Department of Biochemistry, Brandeis University, 415 South Street, Waltham, MA 02454-9110, USA.
| |
Collapse
|
11
|
Tang L, Kwon HJ, Kang KA. Theoretical and experimental analysis of analyte transport in a fiber-optic, protein C immuno-biosensor. Biotechnol Bioeng 2004; 88:869-79. [PMID: 15515165 DOI: 10.1002/bit.20310] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Protein C (PC) is an important anticoagulant in human blood plasma, and early diagnosis of PC deficiency is critical for preventing dangerous thromboembolic complications. A fiber-optic PC immuno-biosensor has been under development in our research group for real-time PC-deficiency diagnosis. The sensor has demonstrated a good sensitivity and specificity for quantifying PC in buffered solutions. However, for plasma samples, with a limited sample reaction time, the sensor produced only 30% of the signal intensity of PC in buffer. The high plasma viscosity (1.9 cP) was speculated as the major reason for signal intensity reduction. In this investigation, the sensing performance of the fiber-optic PC biosensor is systematically characterized in terms of physical and chemical properties of the sample media. Theoretical and experimental analyses indicate that the reduced diffusion rate of PC molecules in viscous samples caused the sensing system to be more mass-transfer-limited. Convective flow of sample/reagent solutions during immunoreactions can increase the rate of the analyte mass transport from the bulk solution to the sensor surface, with reaction kinetics changing from mass-transfer-limited to reaction-limited as flow velocity increases. It was shown that PC sensor performance was significantly improved for plasma samples with convection. The effect of the flow velocity and incubation times for samples and reagents on the sensor performance was also systematically analyzed to optimize the assay protocol for PC sensing. Currently, a 6-cm-long immuno-biosensor is capable of quantifying PC in plasma (1 mL) in the heterozygous PC deficiency range (0.5 to 2.5 microg/mL) within 5 minutes, at an average signal-to-noise ratio of 50.
Collapse
Affiliation(s)
- Liang Tang
- Department of Chemical Engineering, Speed School of Engineering, University of Louisville, Louisville, Kentucky 40292, USA
| | | | | |
Collapse
|
12
|
Orlova EV, Papakosta M, Booy FP, van Heel M, Dolly JO. Voltage-gated K+ channel from mammalian brain: 3D structure at 18A of the complete (alpha)4(beta)4 complex. J Mol Biol 2003; 326:1005-12. [PMID: 12589749 DOI: 10.1016/s0022-2836(02)00708-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Voltage-sensitive K(+) channels (Kv) serve numerous important roles, e.g. in the control of neuron excitability and the patterns of synaptic activity. Here, we use electron microscopy (EM) and single particle analysis to obtain the first, complete structure of Kv1 channels, purified from rat brain, which contain four transmembrane channel-forming alpha-subunits and four cytoplasmically-associated beta-subunits. The 18A resolution structure reveals an asymmetric, dumb-bell-shaped complex with 4-fold symmetry, a length of 140A and variable width. By fitting published X-ray data for recombinant components to our EM map, the modulatory (beta)(4) was assigned to the innermost 105A end, the N-terminal (T1)(4) domain of the alpha-subunit to the central 50A moiety and the pore-containing portion to the 125A membrane part. At this resolution, the selectivity filter could not be localised. Direct contact of the membrane component with the central (T1)(4) domain occurs only via peripheral connectors, permitting communication between the channel and beta-subunits for coupling of responses to changes in excitability and metabolic status of neurons.
Collapse
Affiliation(s)
- Elena V Orlova
- Department of Biological Sciences, Imperial College of Science Technology and Medicine, London SW7 2AY, UK
| | | | | | | | | |
Collapse
|
13
|
Abstract
Potassium channels are multi-subunit complexes, often composed of several polytopic membrane proteins and cytosolic proteins. The formation of these oligomeric structures, including both biogenesis and trafficking, is the subject of this review. The emphasis is on events in the endoplasmic reticulum (ER), particularly on how, where, and when K(+) channel polypeptides translocate and integrate into the bilayer, oligomerize and fold to form pore-forming units, and associate with auxiliary subunits to create the mature channel complex. Questions are raised with respect to the sequence of these events, when biogenic decisions are made, models for integration of K(+) channel transmembrane segments, crosstalk between the cell surface and ER, and recognition of compatible partner subunits. Also considered are determinants of subunit composition and stoichiometry, their consequence for trafficking, mechanisms for ER retention and export, and sequence motifs that direct channels to the cell surface. It is these mechanistic issues that govern the differential distributions of K(+) conductances at the cell surface, and hence the electrical activity of cells and tissues underlying both the physiology and pathophysiology of an organism.
Collapse
Affiliation(s)
- Carol Deutsch
- Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6085, USA.
| |
Collapse
|
14
|
Müller DJ, Janovjak H, Lehto T, Kuerschner L, Anderson K. Observing structure, function and assembly of single proteins by AFM. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2002; 79:1-43. [PMID: 12225775 DOI: 10.1016/s0079-6107(02)00009-3] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Single molecule experiments provide insight into the individuality of biological macromolecules, their unique function, reaction pathways, trajectories and molecular interactions. The exceptional signal-to-noise ratio of the atomic force microscope allows individual proteins to be imaged under physiologically relevant conditions at a lateral resolution of 0.5-1nm and a vertical resolution of 0.1-0.2nm. Recently, it has become possible to observe single molecule events using this technique. This capability is reviewed on various water-soluble and membrane proteins. Examples of the observation of function, variability, and assembly of single proteins are discussed. Statistical analysis is important to extend conclusions derived from single molecule experiments to protein species. Such approaches allow the classification of protein conformations and movements. Recent developments of probe microscopy techniques allow simultaneous measurement of multiple signals on individual macromolecules, and greatly extend the range of experiments possible for probing biological systems at the molecular level. Biologists exploring molecular mechanisms will benefit from a burgeoning of scanning probe microscopes and of their future combination with molecular biological experiments.
Collapse
Affiliation(s)
- Daniel J Müller
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauer Str. 108, D-01307 Dresden, Germany.
| | | | | | | | | |
Collapse
|
15
|
Cahalan MD, Wulff H, Chandy KG. Molecular properties and physiological roles of ion channels in the immune system. J Clin Immunol 2001; 21:235-52. [PMID: 11506193 DOI: 10.1023/a:1010958907271] [Citation(s) in RCA: 187] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The discovery of a diverse and unique set of ion channels in T lymphocytes has led to a rapidly growing body of knowledge about their functional roles in the immune system. Here we review the biophysical and molecular characterization of K+, Ca2+, and Cl- channels in T lymphocytes. Potent and specific blockers, especially of K+ channels, have provided molecular tools to elucidate the involvement of voltage- and calcium-activated potassium channels in T-cell activation and cell-volume regulation. Their unique and differential expression makes lymphocyte K+ channels excellent pharmaceutical targets for modulating immune system function. This review surveys recent progress at the biophysical, molecular, and functional roles of the ion channels found in T lymphocytes.
Collapse
Affiliation(s)
- M D Cahalan
- Department of Physiology and Biophysics, University of California, Irvine 92697, USA.
| | | | | |
Collapse
|
16
|
Lal R, Lin H. Imaging molecular structure and physiological function of gap junctions and hemijunctions by multimodal atomic force microscopy. Microsc Res Tech 2001; 52:273-88. [PMID: 11180620 DOI: 10.1002/1097-0029(20010201)52:3<273::aid-jemt1013>3.0.co;2-m] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Gap junctions are specialized plasma membrane structures that join neighboring cells via specialized intercellular ion channels (hemichannels) and provide a direct pathway for cell-cell communication. They presumably mediate regulation of growth, transmission of developmental signals, coordination of muscle contraction, and maintenance of metabolic homeostasis. Hemichannels are also present in the non-junctional regions of the cell plasma membrane and they provide a direct pathway for communication between the cytoplasm and the extracellular region. Recent studies suggest that gap junctional communication is much more complex than previously anticipated, in terms of both its structure as well as its activity. While the mechanism of gap junction activity is being studied extensively, their quaternary structure, assembly, and conformational changes underlying gating of their activity as well as their physiological role are poorly understood because, due to their complex structure, these junctions are less amenable to existing techniques for high-resolution three-dimensional structure-function analyses. Atomic Force Microscopy (AFM) images molecular structure of biological specimens in an aqueous environment, allows on-line perturbations, and can be coupled with electrophysiological, biochemical, and other microscopic techniques. The present review examines the potential of AFM application for the study of the molecular structure of hydrated, native gap junctions and hemijunctions as well as their physiological functions. Special attention is paid to new, complementary, or provocative findings from AFM studies of both vertebrate and invertebrate gap junctions and hemijunctions.
Collapse
Affiliation(s)
- R Lal
- Neuroscience Research Institute, University of California, Santa Barbara, California 93106, USA.
| | | |
Collapse
|