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Ionic selectivity and thermal adaptations within the voltage-gated sodium channel family of alkaliphilic Bacillus.

DeCaen PG, Takahashi Y, Krulwich TA, Ito M, Clapham DE - Elife (2014)

Bottom Line: Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels.Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria.This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiology, Howard Hughes Medical Institute, Boston Children's Hospital, Boston, United States.

ABSTRACT
Entry and extrusion of cations are essential processes in living cells. In alkaliphilic prokaryotes, high external pH activates voltage-gated sodium channels (Nav), which allows Na(+) to enter and be used as substrate for cation/proton antiporters responsible for cytoplasmic pH homeostasis. Here, we describe a new member of the prokaryotic voltage-gated Na(+) channel family (NsvBa; Non-selective voltage-gated, Bacillus alcalophilus) that is nonselective among Na(+), Ca(2+) and K(+) ions. Mutations in NsvBa can convert the nonselective filter into one that discriminates for Na(+) or divalent cations. Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels. Increasing pH and temperature shifts their activation threshold towards their native resting membrane potential. Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria. This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

No MeSH data available.


Related in: MedlinePlus

Nav steady state voltage-dependence of activation (V1/2) measured in different extracellular pH (pHo) conditions.DOI:http://dx.doi.org/10.7554/eLife.04387.013
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fig5s1: Nav steady state voltage-dependence of activation (V1/2) measured in different extracellular pH (pHo) conditions.DOI:http://dx.doi.org/10.7554/eLife.04387.013

Mentions: Alkaliphilic Bacillus are estimated to have very negative resting membrane potentials (Ψrest ≈ −180 mV), although membrane potentials in bacteria are measured from voltage- sensitive dye studies and variability within populations can be large. Nevertheless, the activation threshold for Bacillus sodium channels is ≈ −40 mV, which is extremely depolarized relative to estimates of Ψrest. Since alkaliphilic bacteria live in high pH environments, we tested whether their sodium channel gating shifted as a function of pH. As shown for the Na+-selective channel from Bacillus pseudofirmus OF4 (NavBp) (Ito et al., 2004), Na+ currents from NaChBac and NsvBa are also modulated by high extracellular pH (Figure 5). When extracellular pH was increased from 7.4 to 9.4, the peak current increased twofold to fourfold and the steady state voltage-dependence was negatively shifted by 28–34 mV (Figure 5—figure supplement 1). Basic extracellular pH alone is probably insufficient to reduce this substantial energy barrier to activate these channels from Ψrest = −180 mV (≈−3.2 kcal/mol). Thus additional influences are required to bring Ψrest and V1/2 closer together.10.7554/eLife.04387.012Figure 5.The bacterial Nav channels are modulated by extracellular alkaline pH (pHo).


Ionic selectivity and thermal adaptations within the voltage-gated sodium channel family of alkaliphilic Bacillus.

DeCaen PG, Takahashi Y, Krulwich TA, Ito M, Clapham DE - Elife (2014)

Nav steady state voltage-dependence of activation (V1/2) measured in different extracellular pH (pHo) conditions.DOI:http://dx.doi.org/10.7554/eLife.04387.013
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4225499&req=5

fig5s1: Nav steady state voltage-dependence of activation (V1/2) measured in different extracellular pH (pHo) conditions.DOI:http://dx.doi.org/10.7554/eLife.04387.013
Mentions: Alkaliphilic Bacillus are estimated to have very negative resting membrane potentials (Ψrest ≈ −180 mV), although membrane potentials in bacteria are measured from voltage- sensitive dye studies and variability within populations can be large. Nevertheless, the activation threshold for Bacillus sodium channels is ≈ −40 mV, which is extremely depolarized relative to estimates of Ψrest. Since alkaliphilic bacteria live in high pH environments, we tested whether their sodium channel gating shifted as a function of pH. As shown for the Na+-selective channel from Bacillus pseudofirmus OF4 (NavBp) (Ito et al., 2004), Na+ currents from NaChBac and NsvBa are also modulated by high extracellular pH (Figure 5). When extracellular pH was increased from 7.4 to 9.4, the peak current increased twofold to fourfold and the steady state voltage-dependence was negatively shifted by 28–34 mV (Figure 5—figure supplement 1). Basic extracellular pH alone is probably insufficient to reduce this substantial energy barrier to activate these channels from Ψrest = −180 mV (≈−3.2 kcal/mol). Thus additional influences are required to bring Ψrest and V1/2 closer together.10.7554/eLife.04387.012Figure 5.The bacterial Nav channels are modulated by extracellular alkaline pH (pHo).

Bottom Line: Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels.Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria.This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiology, Howard Hughes Medical Institute, Boston Children's Hospital, Boston, United States.

ABSTRACT
Entry and extrusion of cations are essential processes in living cells. In alkaliphilic prokaryotes, high external pH activates voltage-gated sodium channels (Nav), which allows Na(+) to enter and be used as substrate for cation/proton antiporters responsible for cytoplasmic pH homeostasis. Here, we describe a new member of the prokaryotic voltage-gated Na(+) channel family (NsvBa; Non-selective voltage-gated, Bacillus alcalophilus) that is nonselective among Na(+), Ca(2+) and K(+) ions. Mutations in NsvBa can convert the nonselective filter into one that discriminates for Na(+) or divalent cations. Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels. Increasing pH and temperature shifts their activation threshold towards their native resting membrane potential. Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria. This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

No MeSH data available.


Related in: MedlinePlus