Person:

Clapham, David

Native PKD2-L1 channel subunits are present in primary cilia and other restricted cellular spaces. Here we investigate the mechanism for the channel's unusual regulation by external calcium, and rationalize this behavior to its specialized function. We report that the human PKD2-L1 selectivity filter is partially selective to calcium ions (Ca2+) moving into the cell, but blocked by high internal Ca2+concentrations, a unique feature of this transient receptor potential (TRP) channel family member. Surprisingly, we find that the C-terminal EF-hands and coiled-coil domains do not contribute to PKD2-L1 Ca2+-induced potentiation and inactivation. We propose a model in which prolonged channel activity results in calcium accumulation, triggering outward-moving Ca2+ ions to block PKD2-L1 in a high-affinity interaction with the innermost acidic residue (D523) of the selectivity filter and subsequent long-term channel inactivation. This response rectifies Ca2+ flow, enabling Ca2+ to enter but not leave small compartments such as the cilium. DOI: http://dx.doi.org/10.7554/eLife.13413.001

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+, Ca2+ 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. DOI: http://dx.doi.org/10.7554/eLife.04387.001