Evidence That Plant K+ Channel Proteins Have Two Different Types of Subunits

Tang, Honglin; Vasconcelos, Aurea C.; Berkowitz, Gerald A.

doi:10.1104/pp.109.1.327

Cited by 45 publications

(35 citation statements)

References 16 publications

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“…In animal systems /3-subunits provide additional mechanisms to diversify K+ channel properties by either modifying inactivation properties or by acting as chaperones (Fink et al, 1996). In plant cells, similar regulatory functions could be fulfilled by hydrophilic subunits: an Arabidopsis homolog to animal K' channel /3-subunits has been identified that may contribute to K+ channel functioning (Tang et al, 1995). Binding of P-subunits to a guard cell membrane protein that is recognized by KATl antibodies supports this hypothesis (Tang et al, 1996).…”

Section: Structure Of Plant K+ Channelssupporting

confidence: 54%

Roles of Higher Plant K+ Channels

Maathuis¹,

Ichida²,

Sanders³

et al. 1997

Plant Physiology

196

123

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Living organisms maintain a cellular solute composition very different from that of the externa1 environment. This implicitly requires the transport of solutes across the cell membrane, and ion channels are integral membrane proteins that play indispensable roles in such transport. In the past dozen years, radical advances have aided in our understanding of ion channel function and regulation in higher plants. Nowhere are these advances more striking than with respect to K+ channels, where the synergistic application of electrophysiological, cell biological, physiological, and molecular techniques has demonstrated an array of channel types playing diverse but defined roles in plant physiology.The major function of K+ channels in animal cells is that of membrane voltage control and short-term repolarization of the membrane. Although K+ channels in plants share similar roles in the regulation of the membrane voltage, early research on guard cells led to the model that shows that plant K+ channels in addition provide important pathways for long-term physiological K+ uptake and release. An extensive range of recent studies suggests diverse longterm transport functions of plant K+ channels, including participation in osmotically driven movements, solute loading into the xylem, cation nutrition, and, by virtue of the presence of K+ channels at endomembranes, intracellular solute redistribution and cytosolic volume control. Most plant K+ channels remain activated for long periods of time, which is critica1 for this proposed long-term transport function of K+ channels in plants. Because higher plant K+ channels are proposed to play a role in regulating both the influx and the efflux of K+ from cells, activity of these channels may impinge upon aspects of turgor and water relations of a11 plant cells. In this Update we focus on important principles of plant K+ channel function and on the proposed physiological roles of specific plant K + channel types in the plasma membrane and tonoplast (Fig. 1A) of different plant cells.

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Section: Structure Of Plant K+ Channelssupporting

confidence: 54%

Roles of Higher Plant K+ Channels

Maathuis¹,

Ichida²,

Sanders³

et al. 1997

Plant Physiology

196

123

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“…Consistent with such loss or divergence reflecting functional adaptations specific to S. cerevisiae, we found instances of functionally related proteins in the set of genes lost from S. cerevisiae, such as the p40 and Int-6 subunits of the translation initiation factor eIF3 (Asano et al 1997 -dependent cell-cell adhesion protein; Wong et al 1996), and a homolog of the mammalian voltage-activated shaker K + channels (e.g., McCormack et al 1995; see Table 4). The presence of homologs of annexin and of shaker K + channels in plants (Tang et al 1995;Braun et al 1998) further supports the view that such genes have been lost from S. cerevisiae, because the plants are likely to represent an outgroup to the animals and fungi (Baldauf and Palmer 1993). Ozier-Kalogeropoulos et al (1998) found that a high percentage of genes from the budding yeast Kluyveromyces lactis were homologs of S. cerevisiae genes previously considered orphans.…”

Section: Genes That Are Lost or Excessively Divergent In S Cerevisiamentioning

confidence: 50%

Large-Scale Comparison of Fungal Sequence Information: Mechanisms of Innovation in Neurospora crassa and Gene Loss in Saccharomyces cerevisiae

Braun

Halpern²,

Nelson³

et al. 2000

Genome Res.

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We report a large-scale comparison of sequence data from the filamentous fungus Neurospora crassa with the complete genome sequence of Saccharomyces cerevisiae. N. crassa is considerably more morphologically and developmentally complex than S. cerevisiae. We found that N. crassa has a much higher proportion of "orphan" genes than S. cerevisiae, suggesting that its morphological complexity reflects the acquisition or maintenance of novel genes, consistent with its larger genome. Our results also indicate the loss of specific genes from S. cerevisiae. Surprisingly, some of the genes lost from S. cerevisiae are involved in basic cellular processes, including translation and ion (especially calcium) homeostasis. Horizontal gene transfer from prokaryotes appears to have played a relatively modest role in the evolution of the N. crassa genome. Differences in the overall rate of molecular evolution between N. crassa and S. cerevisiae were not detected. Our results indicate that the current public sequence databases have fairly complete samples of gene families with ancient conserved regions, suggesting that further sequencing will not substantially change the proportion of genes with homologs among distantly related groups. Models of the evolution of fungal genomes compatible with these results, and their functional implications, are discussed.

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“…KAB1 was cloned as described previously (Tang et al, 1995). For KAT1:KAB1 co-expression experiments, the KAT1 and KAB1 cDNA templates used for cRNA synthesis were subcloned into the pBS-KS II plasmid (Tang et al, 1995).…”

Section: Molecular Biologymentioning

confidence: 99%

“…Prior work has led to the cloning of two plant homologs of animal K ϩ channel ␤-subunits from Arabidopsis (KAB1) (Tang et al, 1995) and rice (Oryza sativa) (KOB1) (Fang et al, 1998). A physical association was demonstrated between the plant K ϩ channel ␤-subunit and a plant ␣-subunit (KAT1) (Tang et al, 1996).…”

mentioning

confidence: 99%

Evaluation of Functional Interaction between K+Channel α- and β-Subunits and Putative Inactivation Gating by Co-Expression in Xenopus laevisOocytes

Zhang

Berkowitz

1999

Plant Physiology

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Animal K؉ channel ␣-(pore-forming) subunits form native proteins by association with ␤-subunits, which are thought to affect channel function by modifying electrophysiological parameters of currents (often by inducing fast inactivation) or by stabilizing the protein complex. We evaluated the functional association of KAT1, a plant K ؉ channel ␣-subunit, and KAB1 (a putative homolog of animal K ؉ channel ␤-subunits) by co-expression in Xenopus laevis oocytes. Oocytes expressing KAT1 displayed inward-rectifying, non-inactivating K ؉ currents that were similar in magnitude to those reported in prior studies. K ؉ currents recorded from oocytes expressing both KAT1 and KAB1 had similar gating kinetics. However, co-expression resulted in greater total current, consistent with the possibility that KAB1 is a ␤-subunit that stabilizes and therefore enhances surface expression of K ؉ channel protein complexes formed by ␣-subunits such as KAT1. K ؉ channel protein complexes formed by ␣-subunits such as KAT1 that undergo (voltagedependent) inactivation do so by means of a "ball and chain" mechanism; the ball portion of the protein complex (which can be formed by the N terminus of either an ␣-or ␤-subunit) occludes the channel pore. KAT1 was co-expressed in oocytes with an animal K ؉ channel ␣-subunit (hKv1.4) known to contain the N-terminal ball and chain. Inward currents through heteromeric hKv1.4:KAT1 channels did undergo typical voltage-dependent inactivation. These results suggest that inward currents through K ؉ channel proteins formed at least in part by KAT1 polypeptides are capable of inactivation, but the structural component facilitating inactivation is not present when channel complexes are formed by either KAT1 or KAB1 in the absence of additional subunits.

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Evidence That Plant K+ Channel Proteins Have Two Different Types of Subunits

Cited by 45 publications

References 16 publications

Roles of Higher Plant K+ Channels

Roles of Higher Plant K+ Channels

Large-Scale Comparison of Fungal Sequence Information: Mechanisms of Innovation in Neurospora crassa and Gene Loss in Saccharomyces cerevisiae

Evaluation of Functional Interaction between K+Channel α- and β-Subunits and Putative Inactivation Gating by Co-Expression in Xenopus laevisOocytes

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