2.A.96.1.1
Acetate/succinate transporter, SatP or YaaH of 196 aas and 6 TMSs (Sá-Pessoa et al. 2013).  It is specific for acetate (a monocarboxylate) and for succinate (a dicarboxylate), with affinity constants at pH 6.0 of 1.24 ± 0.13 mM for acetate and 1.18 ± 0.10 mM for succinate. In glucose grown-cells, the ΔyaaH mutant is compromised for the uptake of both labelled acetic and succinic acids. YaaH, together with ActP, previously described as an acetate transporter, affect the use of acetic acid as a sole carbon and energy source. Both genes have to be deleted simultaneously to abolish acetate transport. The uptake of acetate and succinate was restored when yaaH was expressed in trans in ΔyaaH ΔactP cells. YaaH amino acid residues Leu131 and Ala164 are important for the enhanced ability to transport lactate (Sá-Pessoa et al. 2013). The 3-d structure has been determined to 2.8 Å resolution showing that it is a hexamer with each protomer having a central pore surrounded by 6 TMSs (Sun et al. 2018) (see family description for more details). Wu et al. 2019 suggested that channel opeining involves repacking of key residues, such as Gln50 and Phe17, as well as the subsequent outward movement of all transmembrane helices. Their simulations suggested that acetate is always surrounded by several water molecules when passing through the anion channel, and a high energy barrier of 15 kcal/mol was observed (Wu et al. 2019). SatP from Citrobacter koseri (92% identical to the E. coli ortholog) in liposomes and native nanodiscs has been examined structurally using solid state NMR, revealing the common helical structures in their transmembrane domains (Dong et al. 2021). It is not certain that SatP is a carrier or a channel.