Formate Channels

Formic acid, HCOOH, is an important metabolic intermediate in different pathways. In many microorganisms it is generated from pyruvate, the end product of glycolysis, by the action of a pyruvate:formate lyase. Mammals at this point generate gaseous CO₂ that easily leaves the cell, but in bacteria the formate anion, HCOO^-, requires a dedicated transport system, and the formate channel FocA is used for this task. Enteric bacteria such as Escherichia coli commonly live in an environment rich in sugar and low in oxygen: your gut. Here they gain energy through mixed-acid fermentation, a process that releases the acidic products formate, lactate and acetate and leads to a strong acidification of the environment. The FocA protein is central to this process, as it alone is capable of exporting all these anions to prevent their accumulation in the cell.

References:

• Lü, W., Du, J., Schwarzer, N.J., Gerbig-Smentek, E., Einsle, O. & Andrade, S.L.A. (2012) The formate channel FocA exports the products of mixed-acid fermentation.  Proc. Natl. Acad. Sci. USA, 109, 13254-13259.
• Lü, W., Du, J., Wacker, T., Gerbig-Smentek, E., Andrade, S.L.A. & Einsle, O.(2011) pH-dependent gating in a FocA formate channel.  Science, 332, 352-354.