Pathway · 9 proteins
Ion exchange
Antiporters and other transporters redistribute ions across the membrane.
How it works
- The module is dominated by secondary transporters: a calcium/sodium antiporter, CPA2 and cation:proton antiporters, a cation diffusion facilitator and a ZIP-family metal transporter — all of which exchange or expel ions rather than importing them.
- It also carries an RND-type heavy-metal efflux pump of the CusA/CzcA family with a periplasmic adaptor subunit, and an ABC metal transporter with its solute-binding protein and permease.
- These systems keep cytoplasmic metal concentrations inside narrow limits, and uptake and efflux systems for the same metal commonly coexist because the cell needs both directions. The annotation does not supply affinities or set-points.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Sodium/calcium exchanger membrane region domain-containing protein | — | — | — | 322 | System only |
| ZIP family metal transporter | — | — | — | 243 | System only |
| RCK C-terminal domain-containing protein | — | — | — | 169 | System only |
| Na(+)/H(+) antiporter | — | — | — | 422 | System only |
| Uncharacterized protein | — | — | — | 385 | System only |
| Adhesion protein | — | — | — | 290 | System only |
| NA(+)/H(+) antiporter | — | — | — | 387 | System only |
| Adhesion B | — | — | — | 278 | Step named |
| Na(+)/H(+) antiporter | — | — | — | 408 | System only |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Metal ABC transporter permeaseHome: ATP-coupled transport | — | — | — | 245 | System only |
| Uncharacterized proteinHome: ATP-coupled transport | — | — | — | 243 | System only |
Origins
How could a cell keep its internal salt balance before ion exchangers existed?
Lane and Martin (2012) proposed that early cells at alkaline vents used a sodium/proton antiporter to draw energy from natural gradients.
Deamer lists limits of the vent setting: high salt and divalent ions inhibit membrane assembly, and the proposed natural proton potential has not been demonstrated.
In the cell, exchangers swap ions in fixed ratios to keep sodium out and the internal pH steady. Nine proteins in this pathway do it, and without them the gradients the cell lives on would run down.
From the books: Deamer, Assembling Life, PDF p. 33 and p. 28.
The wider question for this part of the cell: origins for pulling nutrients in from outside.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: ATP-coupled transport · Potassium balance · Channels and ion uptake · Substrate recognition · Not yet placed in a pathway