scholarly journals Structural basis for the channel function of a degraded ABC transporter, CFTR (ABCC7)

2011 ◽  
Vol 138 (5) ◽  
pp. 495-507 ◽  
Author(s):  
Yonghong Bai ◽  
Min Li ◽  
Tzyh-Chang Hwang
Keyword(s):  
Abc Transporter ◽  
Conformational Changes ◽  
Reaction Rates ◽  
Structural Basis ◽  
Helical Axis ◽  
Ion Permeation ◽  
Transmembrane Conductance Regulator ◽  
Channel Opening ◽  
Pore Domain ◽  
Pore Lining

Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily, but little is known about how this ion channel that harbors an uninterrupted ion permeation pathway evolves from a transporter that works by alternately exposing its substrate conduit to the two sides of the membrane. Here, we assessed reactivity of intracellularly applied thiol-specific probes with cysteine residues substituted into the 12th transmembrane segment (TM12) of CFTR. Our experimental data showing high reaction rates of substituted cysteines toward the probes, strong blocker protection of cysteines against reaction, and reaction-induced alterations in channel conductance support the idea that TM12 of CFTR contributes to the lining of the ion permeation pathway. Together with previous work, these findings raise the possibility that pore-lining elements of CFTR involve structural components resembling those that form the substrate translocation pathway of ABC transporters. In addition, comparison of reaction rates in the open and closed states of the CFTR channel leads us to propose that upon channel opening, the wide cytoplasmic vestibule tightens and the pore-lining TM12 rotates along its helical axis. This simple model for gating conformational changes in the inner pore domain of CFTR argues that the gating transition of CFTR and the transport cycle of ABC proteins share analogous conformational changes. Collectively, our data corroborate the popular hypothesis that degradation of the cytoplasmic-side gate turned an ABC transporter into the CFTR channel.

scholarly journals Structural Basis for pH-Gating of the K+ Channel TWIK1 at the Selectivity Filter

2021 ◽  
Author(s):  
Toby S Turney ◽  
Vivian Li ◽  
Stephen G Brohawn
Keyword(s):  
Conformational Changes ◽  
Pancreatic Beta Cells ◽  
Low Ph ◽  
Selectivity Filter ◽  
Structural Basis ◽  
K Channel ◽  
Open Conformation ◽  
Gating Mechanism ◽  
Lipid Nanodiscs ◽  
Pore Domain

TWIK1 is a widely expressed pH-gated two-pore domain K+ channel (K2P) that contributes to cardiac rhythm generation and insulin release from pancreatic beta cells. TWIK1 displays unique properties among K2Ps including low basal activity and inhibition by extracellular protons through incompletely understood mechanisms. Here, we present cryo-EM structures of TWIK1 in lipid nanodiscs at high and low pH that reveal a novel gating mechanism at the K+ selectivity filter. At high pH, TWIK1 adopts an open conformation. At low pH, protonation of an extracellular histidine results in a cascade of conformational changes that close the channel by sealing the top of the selectivity filter, displacing the helical cap to block extracellular ion access pathways, and opening gaps for lipid block of the intracellular cavity. These data provide a mechanistic understanding for extracellular pH-gating of TWIK1 and show how diverse mechanisms have evolved to gate the selectivity filter of K+ channels.

scholarly journals Comparison of Taurine- and Glycine-induced Conformational Changes in the M2-M3 Domain of the Glycine Receptor

2004 ◽  
Vol 279 (19) ◽  
pp. 19559-19565 ◽  
Author(s):  
Nian-Lin R. Han ◽  
John D. Clements ◽  
Joseph W. Lynch
Keyword(s):  
Conformational Changes ◽  
Reaction Rate ◽  
Partial Agonist ◽  
Glycine Receptor ◽  
Reaction Rates ◽  
Structural Basis ◽  
Surface Accessibility ◽  
Partial Agonists ◽  
Substituted Cysteine Accessibility ◽  
Receptor Family

In the ionotropic glutamate receptor, the global conformational changes induced by partial agonists are smaller than those induced by full agonists. However, in the pentameric ligand-gated ion channel receptor family, the structural basis of partial agonism is not understood. This study investigated whether full and partial agonists induce different conformation changes in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility analysis demonstrated previously that glycine binding induced an increase in surface accessibility of all residues from Arg271to Lys276in the M2-M3 domain of the homomeric α1 GlyR. Here we compare the surface accessibility changes induced by the full agonist, glycine, and the partial agonist, taurine. In GlyRs incorporating the A272C, S273C, L274C, or P275C mutation, the reaction rate of the cysteine-specific compound, methanethiosulfonate ethyltrimethylammonium, depended on how strongly the receptors were activated but was agonist-independent. Reaction rates could not be compared in the R271C and K276C mutant GlyRs because methanethiosulfonate ethyltrimethylammonium did not modify the extremely small currents induced by saturating taurine or equivalent low glycine concentrations. The results indicate that bound taurine and glycine molecules impose identical conformational changes to the M2-M3 domain. We therefore conclude that the higher efficacy of glycine is due to an increased ability to stabilize a common activated configuration.

scholarly journals Structure/function studies of CFTR's pore-forming domain reveal evolutionary divergence between CFTR and ABC transporters

2015 ◽  
Author(s):  
◽  
Xiaolong Gao
Keyword(s):  
Cystic Fibrosis ◽  
Structure Function ◽  
Abc Transporter ◽  
Anion Channel ◽  
Site Directed Mutagenesis ◽  
Evolutionary Divergence ◽  
Narrow Region ◽  
Main Components ◽  
Pore Domain ◽  
Pore Lining

Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is the culprit behind Cystic Fibrosis (CF), a genetic disease highly occurs among Caucasians. Studying the structure/function of CFTR chloride channel not only facilitates our understanding of the molecular nature of this protein, but also potentially provides cures for the debilitating disease. In my study, by adopting site-directed mutagenesis and Patch Clamp as well as other various molecular biology techniques, I focused my efforts in CFTR's pore domain and made the following revealing findings: First, the first transmembrane segment (TM1) contributes to CFTR's pore lining with its whole length and the restrictive region identified in TM1 confirms that CFTR's pore is constituted by three main components: a narrow region flanked by the internal and external vestibules. Second, while TM1 and TM6 contribute to pore lining for CFTR in a relatively symmetrical manner, a lack of symmetry between TM6 and its topological counterpart -- TM12 suggests the two-fold pseudo-symmetry seen with other ABC proteins does not apply in CFTR's TMDs. At last, the gate of CFTR resides in a region (337 -- 344 in TM6) that encompasses the above mentioned narrow region (338- 341 in TM6) which may also serve as the selectivity filter for this anion channel, challenging the prevailing degraded ABC transporter hypothesis that states CFTR evolves from an ABC transporter by simply degenerating the intracellular gate.

scholarly journals Structural basis for ion selectivity in TMEM175 K+ channels

2018 ◽  
Author(s):  
Janine D. Brunner ◽  
Roman P. Jakob ◽  
Tobias Schulze ◽  
Yvonne Neldner ◽  
Anna Moroni ◽  
...  
Keyword(s):  
Ion Selectivity ◽  
Structural Basis ◽  
Channel Pore ◽  
K Channels ◽  
X Ray ◽  
Selective Filter ◽  
Channel Opening ◽  
Conformational Rearrangements ◽  
Pore Lining ◽  
Conductive State

AbstractThe TMEM175 family constitutes recently discovered K+ channels that lack signatures for a P-loop selectivity filter, a hallmark of all known K+ channels. This raises the question how selectivity in TMEM175 channels is achieved. Here we report the X-ray structure of a bacterial TMEM175 family member in complex with a novel chaperone built of a nanobody fusion-protein. The structure of the channel in a non-conductive conformation was solved at 2.4 Å and revealed bound K+ ions along the channel pore. A hydrated K+ ion at the extracellular pore entrance that could be substituted with Cs+ and Rb+ is coordinated by backbone-oxygens forming a cation-selective filter at the tip of the pore-lining helices. Another K+ ion within the pore indicates the passage of dehydrated ions. Unexpectedly, a highly conserved threonine residue deeper in the pore conveys the K+ selectivity. The position of this threonine in the non-conductive state suggests major conformational rearrangements of the pore-lining helices for channel opening, possibly involving iris-like motions.

scholarly journals Structural basis for activation and gating of IP3 receptors

2021 ◽  
Author(s):  
Emily A Schmitz ◽  
Hirohide Takahashi ◽  
Erkan Karakas
Keyword(s):  
Conformational Changes ◽  
Molecular Mechanisms ◽  
Receptor Activation ◽  
Structural Basis ◽  
Ip3 Receptors ◽  
Cellular Processes ◽  
Cryo Electron Microscopy ◽  
Channel Opening ◽  
High Concentrations ◽  
Type 3

Calcium (Ca2+) is a universal and versatile cellular messenger used to regulate numerous cellular processes in response to external or internal stimuli. A pivotal component of the Ca2+ signaling toolbox in cells is the inositol 1,4,5-triphosphate (IP3) receptors (IP3Rs), which mediate Ca2+ release from the endoplasmic reticulum (ER), controlling cytoplasmic and organellar Ca2+ concentrations. IP3Rs are activated by IP3 and Ca2+, inhibited by Ca2+ at high concentrations, and potentiated by ATP1-3. However, the underlying molecular mechanisms are unclear due to the lack of structures in the active conformation. Here we report cryo-electron microscopy (cryo-EM) structures of human type-3 IP3R in multiple gating conformations; IP3-ATP bound pre-active states with closed channels, IP3-ATP-Ca2+ bound active state with an open channel, and IP3-ATP-Ca2+ bound inactive state with a closed channel. The structures demonstrate how IP3-induced conformational changes prime the receptor for activation by Ca2+, how Ca2+ binding leads to channel opening, and how ATP modulates the activity, providing insights into the long-sought questions regarding the molecular mechanism of the receptor activation and gating.

Electron Microscopy and image reconstruction reveal the structural basis for spectrin's elastic properties

1992 ◽  
Vol 50 (1) ◽  
pp. 510-511
Author(s):  
Amy M. McGough ◽  
Robert Josephs
Keyword(s):  
Electron Microscopy ◽  
Elastic Properties ◽  
Conformational Changes ◽  
Quaternary Structure ◽  
Three Dimensional ◽  
Membrane Skeleton ◽  
Projection Algorithm ◽  
Structural Basis ◽  
Iterative Approximation ◽  
Membrane Skeletons

The remarkable deformability of the erythrocyte derives in large part from the elastic properties of spectrin, the major component of the membrane skeleton. It is generally accepted that spectrin's elasticity arises from marked conformational changes which include variations in its overall length (1). In this work the structure of spectrin in partially expanded membrane skeletons was studied by electron microscopy to determine the molecular basis for spectrin's elastic properties. Spectrin molecules were analysed with respect to three features: length, conformation, and quaternary structure. The results of these studies lead to a model of how spectrin mediates the elastic deformation of the erythrocyte.Membrane skeletons were isolated from erythrocyte membrane ghosts, negatively stained, and examined by transmission electron microscopy (2). Particle lengths and end-to-end distances were measured from enlarged prints using the computer program MACMEASURE. Spectrin conformation (straightness) was assessed by calculating the particles’ correlation length by iterative approximation (3). Digitised spectrin images were correlation averaged or Fourier filtered to improve their signal-to-noise ratios. Three-dimensional reconstructions were performed using a suite of programs which were based on the filtered back-projection algorithm and executed on a cluster of Microvax 3200 workstations (4).

Crystal structures of Magnaporthe oryzae trehalose-6-phosphate synthase (MoTps1) suggest a model for catalytic process of Tps1

2019 ◽  
Vol 476 (21) ◽  
pp. 3227-3240 ◽  
Author(s):  
Shanshan Wang ◽  
Yanxiang Zhao ◽  
Long Yi ◽  
Minghe Shen ◽  
Chao Wang ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Conformational Changes ◽  
Magnaporthe Oryzae ◽  
Structural Information ◽  
Complex Structure ◽  
Critical Role ◽  
Catalytic Process ◽  
Structural Basis ◽  
Salt Bridges ◽  
Terminal Domain

Trehalose-6-phosphate (T6P) synthase (Tps1) catalyzes the formation of T6P from UDP-glucose (UDPG) (or GDPG, etc.) and glucose-6-phosphate (G6P), and structural basis of this process has not been well studied. MoTps1 (Magnaporthe oryzae Tps1) plays a critical role in carbon and nitrogen metabolism, but its structural information is unknown. Here we present the crystal structures of MoTps1 apo, binary (with UDPG) and ternary (with UDPG/G6P or UDP/T6P) complexes. MoTps1 consists of two modified Rossmann-fold domains and a catalytic center in-between. Unlike Escherichia coli OtsA (EcOtsA, the Tps1 of E. coli), MoTps1 exists as a mixture of monomer, dimer, and oligomer in solution. Inter-chain salt bridges, which are not fully conserved in EcOtsA, play primary roles in MoTps1 oligomerization. Binding of UDPG by MoTps1 C-terminal domain modifies the substrate pocket of MoTps1. In the MoTps1 ternary complex structure, UDP and T6P, the products of UDPG and G6P, are detected, and substantial conformational rearrangements of N-terminal domain, including structural reshuffling (β3–β4 loop to α0 helix) and movement of a ‘shift region' towards the catalytic centre, are observed. These conformational changes render MoTps1 to a ‘closed' state compared with its ‘open' state in apo or UDPG complex structures. By solving the EcOtsA apo structure, we confirmed that similar ligand binding induced conformational changes also exist in EcOtsA, although no structural reshuffling involved. Based on our research and previous studies, we present a model for the catalytic process of Tps1. Our research provides novel information on MoTps1, Tps1 family, and structure-based antifungal drug design.

scholarly journals Structural basis for activation and allosteric modulation of full-length calcium-sensing receptor

2021 ◽  
Vol 7 (23) ◽  
pp. eabg1483
Author(s):  
Tianlei Wen ◽  
Ziyu Wang ◽  
Xiaozhe Chen ◽  
Yue Ren ◽  
Xuhang Lu ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Bound States ◽  
Hormone Secretion ◽  
Allosteric Modulation ◽  
Full Length ◽  
Structural Basis ◽  
Endocrine Disorders ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Class C

Calcium-sensing receptor (CaSR) is a class C G protein–coupled receptor (GPCR) that plays an important role in calcium homeostasis and parathyroid hormone secretion. Here, we present multiple cryo–electron microscopy structures of full-length CaSR in distinct ligand-bound states. Ligands (Ca2+ and l-tryptophan) bind to the extracellular domain of CaSR and induce large-scale conformational changes, leading to the closure of two heptahelical transmembrane domains (7TMDs) for activation. The positive modulator (evocalcet) and the negative allosteric modulator (NPS-2143) occupy the similar binding pocket in 7TMD. The binding of NPS-2143 causes a considerable rearrangement of two 7TMDs, forming an inactivated TM6/TM6 interface. Moreover, a total of 305 disease-causing missense mutations of CaSR have been mapped to the structure in the active state, creating hotspot maps of five clinical endocrine disorders. Our results provide a structural framework for understanding the activation, allosteric modulation mechanism, and disease therapy for class C GPCRs.

New insights into the structural basis of integrin activation

Blood ◽  
2003 ◽  
Vol 102 (4) ◽  
pp. 1155-1159 ◽  
Author(s):  
Jian-Ping Xiong ◽  
Thilo Stehle ◽  
Simon L. Goodman ◽  
M. Amin Arnaout
Keyword(s):  
Conformational Changes ◽  
Structural Changes ◽  
Structural Basis ◽  
Integrin Activation ◽  
Cellular Functions ◽  
Electron Microscopic ◽  
The Past ◽  
Intracellular Signals ◽  
Bidirectional Signaling ◽  
New Hypothesis

Abstract Integrins are cell adhesion receptors that communicate biochemical and mechanical signals in a bidirectional manner across the plasma membrane and thus influence most cellular functions. Intracellular signals switch integrins into a ligand-competent state as a result of elicited conformational changes in the integrin ectodomain. Binding of extracellular ligands induces, in turn, structural changes that convey distinct signals to the cell interior. The structural basis of this bidirectional signaling has been the focus of intensive study for the past 3 decades. In this perspective, we develop a new hypothesis for integrin activation based on recent crystallographic, electron microscopic, and biochemical studies.

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