scholarly journals Structural basis for C-type inactivation in a Shaker family voltage gated K+ channel

2021 ◽  
Author(s):  
Ravikumar Reddi ◽  
Kimberly Matulef ◽  
Erika A. Riederer ◽  
Matthew R. Whorton ◽  
Francis I. Valiyaveetil
Keyword(s):  
Crystal Structure ◽  
Binding Sites ◽  
Structural Changes ◽  
Selectivity Filter ◽  
Structural Basis ◽  
K Channel ◽  
Ion Binding ◽  
Channel Pore ◽  
Voltage Gated ◽  
Ion Binding Sites

AbstractC-type inactivation is a process by which ion flux through a voltage-gated K+ (Kv) channel is regulated at the selectivity filter. While prior studies have indicated that C-type inactivation involves structural changes at the selectivity filter, the nature of the changes have not been resolved. Here we report the crystal structure of the Kv1.2 channel in a C-type inactivated state. The structure shows that C-type inactivation involves changes in the selectivity filter that disrupt the outer two ion binding sites in the filter. The changes at the selectivity filter propagate to the extracellular mouth and the turret regions of the channel pore. The structural changes observed are consistent with the functional hallmarks of C-type inactivation. This study highlights the intricate interplay between K+ occupancy at the ion binding sites and the interactions of the selectivity filter in determining the balance between the conductive and the inactivated conformations of the filter.

scholarly journals Structural basis of ion transport and inhibition in ferroportin

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Yaping Pan ◽  
Zhenning Ren ◽  
Shuai Gao ◽  
Jiemin Shen ◽  
Lie Wang ◽  
...  
Keyword(s):  
Binding Sites ◽  
Metal Ion ◽  
Peptide Hormone ◽  
Structural Basis ◽  
Deficiency Anemia ◽  
Pharmacological Intervention ◽  
Ion Binding ◽  
Coupled Transport ◽  
Metal Ion Binding ◽  
Ion Binding Sites

Abstract Ferroportin is an iron exporter essential for releasing cellular iron into circulation. Ferroportin is inhibited by a peptide hormone, hepcidin. In humans, mutations in ferroportin lead to ferroportin diseases that are often associated with accumulation of iron in macrophages and symptoms of iron deficiency anemia. Here we present the structures of the ferroportin from the primate Philippine tarsier (TsFpn) in the presence and absence of hepcidin solved by cryo-electron microscopy. TsFpn is composed of two domains resembling a clamshell and the structure defines two metal ion binding sites, one in each domain. Both structures are in an outward-facing conformation, and hepcidin binds between the two domains and reaches one of the ion binding sites. Functional studies show that TsFpn is an electroneutral H+/Fe2+ antiporter so that transport of each Fe2+ is coupled to transport of two H+ in the opposite direction. Perturbing either of the ion binding sites compromises the coupled transport of H+ and Fe2+. These results establish the structural basis of metal ion binding, transport and inhibition in ferroportin and provide a blueprint for targeting ferroportin in pharmacological intervention of ferroportin diseases.

scholarly journals Structural basis of ion permeation gating in Slo2.1 K+ channels

2013 ◽  
Vol 142 (5) ◽  
pp. 523-542 ◽  
Author(s):  
Priyanka Garg ◽  
Alison Gardner ◽  
Vivek Garg ◽  
Michael C. Sanguinetti
Keyword(s):  
Selectivity Filter ◽  
Structural Basis ◽  
K Channel ◽  
Xenopus Laevis Oocytes ◽  
Ion Permeation ◽  
Channel Activation ◽  
K Channels ◽  
Voltage Gated ◽  
Channel Function ◽  
Activation Gate

The activation gate of ion channels controls the transmembrane flux of permeant ions. In voltage-gated K+ channels, the aperture formed by the S6 bundle crossing can widen to open or narrow to close the ion permeation pathway, whereas the selectivity filter gates ion flux in cyclic-nucleotide gated (CNG) and Slo1 channels. Here we explore the structural basis of the activation gate for Slo2.1, a weakly voltage-dependent K+ channel that is activated by intracellular Na+ and Cl−. Slo2.1 channels were heterologously expressed in Xenopus laevis oocytes and activated by elevated [NaCl]i or extracellular application of niflumic acid. In contrast to other voltage-gated channels, Slo2.1 was blocked by verapamil in an activation-independent manner, implying that the S6 bundle crossing does not gate the access of verapamil to its central cavity binding site. The structural basis of Slo2.1 activation was probed by Ala scanning mutagenesis of the S6 segment and by mutation of selected residues in the pore helix and S5 segment. Mutation to Ala of three S6 residues caused reduced trafficking of channels to the cell surface and partial (K256A, I263A, Q273A) or complete loss (E275A) of channel function. P271A Slo2.1 channels trafficked normally, but were nonfunctional. Further mutagenesis and intragenic rescue by second site mutations suggest that Pro271 and Glu275 maintain the inner pore in an open configuration by preventing formation of a tight S6 bundle crossing. Mutation of several residues in S6 and S5 predicted by homology modeling to contact residues in the pore helix induced a gain of channel function. Substitution of the pore helix residue Phe240 with polar residues induced constitutive channel activation. Together these findings suggest that (1) the selectivity filter and not the bundle crossing gates ion permeation and (2) dynamic coupling between the pore helix and the S5 and S6 segments mediates Slo2.1 channel activation.

scholarly journals Crystal Structure of Calcium-free α-Amylase fromBacillussp. Strain KSM-K38 (AmyK38) and Its Sodium Ion Binding Sites

2003 ◽  
Vol 278 (27) ◽  
pp. 24818-24824 ◽  
Author(s):  
Tsuyoshi Nonaka ◽  
Masahiro Fujihashi ◽  
Akiko Kita ◽  
Hiroshi Hagihara ◽  
Katsuya Ozaki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Binding Sites ◽  
Sodium Ion ◽  
Ion Binding ◽  
Ion Binding Sites

scholarly journals High-resolution crystal structure ofStreptococcus agalactiaeglyceraldehyde-3-phosphate dehydrogenase

2018 ◽  
Vol 74 (4) ◽  
pp. 236-244 ◽  
Author(s):  
Kang Zhou ◽  
Xiaojiao Fan ◽  
Yuelong Li ◽  
Caiying Zhang ◽  
Tengchuan Jin
Keyword(s):  
Crystal Structure ◽  
Binding Sites ◽  
Pathogenic Bacteria ◽  
Catalytic Mechanism ◽  
Group B Streptococcus ◽  
Ion Binding ◽  
Phosphate Ion ◽  
Ion Binding Sites ◽  
Group B ◽  
Shed Light

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme that plays critical roles in bacterial pathogenesis in some pathogenic bacteria. In this study, the crystal structure of group B streptococcus GAPDH was determined at 1.36 Å resolution. The structure contained an asymmetric mixed holo tetramer, with two NAD ligands bound to two protomers. Further structural analysis identified interesting phosphate ion-binding sites, which shed light on its catalytic mechanism.

scholarly journals Individual Ion Binding Sites in the K+ Channel Play Distinct Roles in C-type Inactivation and in Recovery from Inactivation

Structure ◽  
2016 ◽  
Vol 24 (5) ◽  
pp. 750-761 ◽  
Author(s):  
Kimberly Matulef ◽  
Alvin W. Annen ◽  
Jay C. Nix ◽  
Francis I. Valiyaveetil
Keyword(s):  
Binding Sites ◽  
K Channel ◽  
Ion Binding ◽  
Individual Ion ◽  
Recovery From Inactivation ◽  
Ion Binding Sites

scholarly journals Divalent cation block and competition between divalent and monovalent cations in the large-conductance K+ channel from Chara australis.

1992 ◽  
Vol 100 (2) ◽  
pp. 269-300 ◽  
Author(s):  
D R Laver
Keyword(s):  
Binding Sites ◽  
K Channel ◽  
Ion Binding ◽  
Patch Clamp Technique ◽  
Ion Specificity ◽  
Ion Interactions ◽  
Chara Australis ◽  
Ion Binding Sites ◽  
A Site ◽  
Cytoplasmic Side

The patch-clamp technique is used to investigate divalent ion block of the large-conductance K+ channel from Chara australis. Block by Ba2+, Ca2+, Mg2+, and Pt(NH3)4(2+) from the vacuolar and cytoplasmic sides is used to probe the structure of, and ion interactions within, the pore. Five divalent ion binding sites are detected. Vacuolar Ca2+ reduces channel conductance by binding to a site located 7% along the membrane potential difference (site 1, delta = 0.07; from the vacuolar side); it also causes channel closures with mean a duration of approximately 0.1-1 ms by binding at a deeper site (site 2, delta = 0.3). Ca2+ can exit from site 2 into both the vacuolar and cytoplasmic solutions. Cytoplasmic Ca2+ reduces conductance by binding at two sites (site 3, delta = -0.21; site 4, delta = -0.6; from the cytoplasmic side) and causes closures with a mean duration of 10-100 ms by binding to site 5 (delta = -0.7). The deep sites exhibit stronger ion specificity than the superficial sites. Cytoplasmic Ca2+ binds sequentially to sites 3-5 and Ca2+ at site 5 can be locked into the pore by a second Ca2+ at site 3 or 4. Ca2+ block is alleviated by increasing [K+] on the same side of the channel. Further, Ca2+ occupancy of the deep sites (2, 4, and 5) is reduced by K+, Rb+, NH4+, and Na+ on the opposite side of the pore. Their relative efficacy correlates with their relative permeability in the channel. While some Ca2+ and K+ sites compete for ions, Ca2+ and K+ can simultaneously occupy the channel. Ca2+ binding at site 1 only partially blocks channel conduction. The results suggest the presence of four K+ binding sites on the channel protein. One cytoplasmic facing site has an equilibrium affinity of 10 mM (site 6, delta = -0.3) and one vacuolar site (site 7, delta less than 0.2) has low affinity (greater than 500 mM). Divalent ion block of the Chara channel shows many similarities to that of the maxi-K channel from rat skeletal muscle.

scholarly journals Accessibility of Cations to the Selectivity Filter of KcsA in the Inactivated State: An Equilibrium Binding Study

2019 ◽  
Vol 20 (3) ◽  
pp. 689 ◽  
Author(s):  
Ana Giudici ◽  
Maria Renart ◽  
Clara Díaz-García ◽  
Andrés Morales ◽  
José Poveda ◽  
...  
Keyword(s):  
Potassium Channel ◽  
Binding Sites ◽  
Cation Binding ◽  
Selectivity Filter ◽  
Ion Binding ◽  
Channel State ◽  
Equilibrium Conditions ◽  
Equilibrium Binding ◽  
Potassium Channel Kcsa ◽  
Ion Binding Sites

Cation binding under equilibrium conditions has been used as a tool to explore the accessibility of permeant and nonpermeant cations to the selectivity filter in three different inactivated models of the potassium channel KcsA. The results show that the stack of ion binding sites (S1 to S4) in the inactivated filter models remain accessible to cations as they are in the resting channel state. The inactivated state of the selectivity filter is therefore “resting-like” under such equilibrium conditions. Nonetheless, quantitative differences in the apparent KD’s of the binding processes reveal that the affinity for the binding of permeant cations to the inactivated channel models, mainly K+, decreases considerably with respect to the resting channel. This is likely to cause a loss of K+ from the inactivated filter and consequently, to promote nonconductive conformations. The most affected site by the affinity loss seems to be S4, which is interesting because S4 is the first site to accommodate K+ coming from the channel vestibule when K+ exits the cell. Moreover, binding of the nonpermeant species, Na+, is not substantially affected by inactivation, meaning that the inactivated channels are also less selective for permeant versus nonpermeant cations under equilibrium conditions.

scholarly journals Ion Binding Sites and Hydration in the Selectivity Filter of the Bacterial Sodium Channel Navab

2012 ◽  
Vol 102 (3) ◽  
pp. 603a
Author(s):  
Vincenzo Carnevale ◽  
Werner Treptow ◽  
Michael L. Klein
Keyword(s):  
Sodium Channel ◽  
Binding Sites ◽  
Selectivity Filter ◽  
Ion Binding ◽  
Ion Binding Sites

scholarly journals Crystal Structure of a Voltage-gated K+Channel Pore Module in a Closed State in Lipid Membranes

2012 ◽  
Vol 287 (51) ◽  
pp. 43063-43070 ◽  
Author(s):  
Jose S. Santos ◽  
Guillermo A. Asmar-Rovira ◽  
Gye Won Han ◽  
Wei Liu ◽  
Ruhma Syeda ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Lipid Membranes ◽  
K Channel ◽  
Channel Pore ◽  
Voltage Gated ◽  
Closed State
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