The Kv7.2/Kv7.3 Heterotetramer Assembles with a Random Subunit Arrangement

Stewart, Andrew P.; Gómez-Posada, Juan Camilo; McGeorge, Jessica; Rouhani, Maral; Villarroel, Álvaro; Murrell‐Lagnado, Ruth D.; Edwardson, J. Michael

doi:10.1074/jbc.m111.336511

Cited by 21 publications

(23 citation statements)

References 34 publications

(43 reference statements)

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“…This mutation at the first position of the selectivity filter signature (GYG) exerts a dominant‐negative effect . Accordingly, no currents were observed when combined with Kv7.3, but when expressed with both Kv7.2 and Kv7.3, current levels were recovered, which, taking into account the random assembly of subunits, suggest that the incorporation of 2 mutated subunits is required to abolish current in Kv7.2/Kv7.3 heterotetramers. Similarly, the E130K mutant exerted a dominant‐negative effect with Kv7.2, but not when expressed with Kv7.2 and Kv7.3.…”

Section: Discussionmentioning

confidence: 99%

Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy

et al. 2018

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Objective: To gain insight into the mechanisms underlying KCNQ2 encephalopathy by examining the electrophysiologic properties of mutant Kv7.2 channels in different multimeric configurations. Methods: We analyzed the genotype-phenotype relationship in 4 patients with KCNQ2 encephalopathy and performed electrophysiologic analysis of M-currents mediated by homomeric Kv7.2 or heteromeric Kv7.2/Kv7.3 channels.Results: Negligible or no current was recorded in cells expressing homomeric E130K, W270R, or G281R de novo mutants, and it was reduced by more than 90% for the L243F maternally inherited mutant. The E130K and G281R mutants presented a marked dominant-negative behavior, whereas the current density was partially reduced (L243F) or not affected (W270R) when coexpressed with wildtype Kv7.2 subunits. In contrast, the extent of Kv7.3 "rescue," which yields negligible currents on its own, followed the sequence E130K > L243F > W270R, whereas no rescue was observed with the G281R mutant. No significant effects on current density were observed when subunits were expressed in a 0.5:0.5:1.0 (Kv7.2:mutant:Kv7.3) DNA ratio to mimic the genetic balance. There was an increase in sensitivity to phosphatidylinositol 4,5-bisphosphate (PIP 2 ) depletion for W270R/Kv7.3, but no substantial differences were observed when the mutated subunits were coexpressed with Kv7.2 or both Kv7.2 and Kv7.3. Significance: There was a marked disparity of the impact of these mutations on Kv7.2 function, which varied on association with Kv7.2 or Kv7.3 subunits. Current density of homomeric channels was the most reliable property relating Kv7.2 function to encephalopathy, but other factors are required to explain the milder phenotype for some individuals carrying the maternally inherited L243F mutation.We hypothesize that the role of homomeric Kv7.2 channels for fine-tuning neuronal connections during development is critical for the severity of the KCNQ2 encephalopathy. K E Y W O R D Searly infantile epileptic encephalopathies, epilepsy, KCNQ2, M-current, PIP 2

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Section: Discussionmentioning

confidence: 99%

Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy

et al. 2018

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“…Studies of a variety of channels and receptors have shown that subunit arrangement in the conformation of heterooligomers varies depending on which membrane protein is being analyzed. It has been proposed that individual proteins might assemble with a random arrangement that is dependent on their abundance (40)(41)(42)(43), with a random arrangement of preformed homomeric dimers (44), and some channels even assemble as heteromeric structures with fixed stoichiometry (45,46). With respect to aquaporins, it was reported that the AQP4 isoforms M1 and M23 seem to assemble as heterotetramers with a random arrangement (47).…”

Section: Discussionmentioning

confidence: 99%

Heteromerization of PIP aquaporins affects their intrinsic permeability

Yaneff

Sigaut

Marquez

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The plant aquaporin plasma membrane intrinsic proteins (PIP) subfamily represents one of the main gateways for water exchange at the plasma membrane (PM). A fraction of this subfamily, known as PIP1, does not reach the PM unless they are coexpressed with a PIP2 aquaporin. Although ubiquitous and abundantly expressed, the role and properties of PIP1 aquaporins have therefore remained masked. Here, we unravel how FaPIP1;1, a fruit-specific PIP1 aquaporin from Fragaria x ananassa, contributes to the modulation of membrane water permeability (P f ) and pH aquaporin regulation. Our approach was to combine an experimental and mathematical model design to test its activity without affecting its trafficking dynamics. We demonstrate that FaPIP1;1 has a high water channel activity when coexpressed as well as how PIP1-PIP2 affects gating sensitivity in terms of cytosolic acidification. PIP1-PIP2 random heterotetramerization not only allows FaPIP1;1 to arrive at the PM but also produces an enhancement of FaPIP2;1 activity. In this context, we propose that FaPIP1;1 is a key participant in the regulation of water movement across the membranes of cells expressing both aquaporins.T he plasma membrane (PM) is the first barrier that limits water exchange in plant cells. The rate of its water transport capacity is mainly associated with aquaporins. Among the seven aquaporin subfamilies described in the plant kingdom, only plasma membrane intrinsic proteins (PIP) and some members of the nodulin-26-like intrinsic proteins (NIP) and X intrinsic proteins (XIP) subfamilies have been shown to be preferentially localized at the PM (1, 2). Of these, PIP aquaporins appear to have a large role in controlling membrane water permeability, whereas NIP and XIP have been mainly described as solute transporters (2-4). Plant PIP aquaporins represent a conserved subfamily that has been historically divided into two subgroups due to their differences in primary structure, PIP1 and PIP2. Interestingly, PIP aquaporins compose ∼40% of the total aquaporin set, and the PIP1 and PIP2 ratio among different species is relatively constant (5-12). Fig. S1 shows the distribution of all aquaporin genes present in plants whose genome has been completely sequenced and analyzed. Antisense inhibition experiments on Arabidopsis thaliana PIP1 and PIP2 have suggested that the two subgroups of aquaporins contribute to root or leaf hydraulic conductivity in the same way (13). In several plant species, members of the PIP1 and PIP2 subgroups were shown to be coexpressed in the same cell type (14-17).Although PIP1 are as ubiquitous as PIP2, the functional properties of each type of channel are different. PIP2 are very well described as a homotetramer with high water transport activity (18, 19) and a gating mechanism unequivocally associated with specific and conserved amino acid motifs triggered by cytosolic acidification (20-22), phosphorylation (23, 24), or divalent cation concentration (22). In contrast, PIP1 have shown complex heterogeneity in water and solute transpor...

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“…A fixed stoichiometry and subunit arrangement have been reported for transient receptor potential channels, where the co-expression of TRPP (polycystin) (TRPP2) and TRPC (canonical) (TRPC1) subunits formed heteromeric channels with a 2 : 2 stoichiometry and subunits arranged alternately within the tetramer (Kobori et al, 2009;Stewart et al, 2010). In contrast, it has been proposed that heteromeric KCNQ (Kv7) channels display variable stoichiometry, with subunits arranged randomly (Stewart et al, 2012). These data indicate that a fixed stoichiometry and arrangement of subunits within a channel tetramer might be common and would suggest that the diversity of potassium and other channels might not be as large as originally thought (Jan & Jan, 1990).…”

Section: Discussionmentioning

confidence: 99%

Preferential assembly of heteromeric small conductance calcium‐activated potassium channels

Church

Weatherall

Corrêa

et al. 2014

Eur J of Neuroscience

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The activation of small conductance calcium‐dependent (SK) channels regulates membrane excitability by causing membrane hyperpolarization. Three subtypes (SK1‐3) have been cloned, with each subtype expressed within the nervous system. The locations of channel subunits overlap, with SK1 and SK2 subunits often expressed in the same brain region. We showed that expressed homomeric rat SK1 subunits did not form functional channels, because subunits accumulated in the Golgi. This raised the question of whether heteromeric channels could form with SK1 subunits. The co‐expression of SK1 and SK2 subunits in HEK293 cells preferentially co‐assembled to produce heteromeric channels with a fixed stoichiometry of alternating subunits. The expression in hippocampal CA1 neurons of mutant rat SK1 subunits [rat SK1(LV213/4YA)] that produced an apamin‐sensitive current changed the amplitude and pharmacology of the medium afterhyperpolarization. The overexpression of rat SK1(LV213/4YA) subunits reduced the sensitivity of the medium afterhyperpolarization to apamin, substantiating the preferential co‐assembly of SK1 and SK2 subunits to form heteromeric channels. Species‐specific channel assembly occurred as the co‐expression of human SK1 with rat SK2 did not form functional heteromeric channels. The replacement of two amino acids within the C‐terminus of rat SK2 with those from human SK2 permitted the assembly of heteromeric channels when co‐expressed with human SK1. These data showed that species‐specific co‐assembly was mediated by interaction between the C‐termini of SK channel subunits. The finding that SK channels preferentially co‐assembled to form heteromeric channels suggested that native heteromeric channels will predominate in cells expressing multiple SK channel subunits.

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The Kv7.2/Kv7.3 Heterotetramer Assembles with a Random Subunit Arrangement

Abstract: Background: Kv7.2 and Kv7.3 coassemble to form a heteromeric K ϩ channel that generates the M-current.

Cited by 21 publications

References 34 publications

Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy

Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy

Heteromerization of PIP aquaporins affects their intrinsic permeability

Preferential assembly of heteromeric small conductance calcium‐activated potassium channels

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