2.A.46 The Benzoate:H Symporter (BenE) Family

The BenE family contains several functionally characterized and sequenced members.  Two of these are the benzoate permeases of Acinetobacter calcoaceticus (Acinetobacter baylyi) and E. coli. These proteins are about 400 residues in length and possibly span the membrane 12 times. They exhibit about 30% identity to each other and limited sequence similarity to members of the aromatic acid:H⁺ symporter (AAHS) family (2.A.1.15) of the major facilitator superfamily (MFS). However the degree of similarity with the latter proteins is insufficient to establish homology. However, the BenE family has been shown to be a member of the APC superfamily. BenE is a Na⁺ symporter (). The ortholog in Pseudomonas putida (Arthrobacter siderocapsulatus)   has also been shown to be a benzoate transporter (Choudhary et al. 2017).

The purine transporter, PurT_Cp of Colwellia psychrerythraea, forms a homodimer, and each protomer has 14 TMSs folded into a transport domain (core domain) and a scaffold domain (gate domain) (Weng et al. 2023). A purine base is present in the structure and defines the location of the substrate binding site. Functional studies reveal that PurT_Cp transports purines but not pyrimidines and that purine binding and transport is dependent on the pH. Mutation of a conserved aspartate residue close to the substrate binding site reveals the critical role of this residue in H⁺-dependent transport of purines. Comparison of the PurT_Cp structure with transporters of the same structural fold suggests that rigid-body motions of the substrate-binding domain are central for substrate translocation across the membrane (Weng et al. 2023).

The generalized transport reactions catalyzed by membres of the BenE family are:

Benzoate (out) + Na⁺ (out) → benzoate (in) +  Na⁺ (in)

purine (out) + H⁺ (out) → purine (in) + H⁺(in)