Fig. 3.

VNUT is an ATP transporter. a (Top) A large-scale expression vector for VNUT in E. coli. For details, see ref. [40]. (Bottom) VNUT proteins purified from insect cells (left) or E. coli (right) were subjected to SDS gel electrophoresis and then stained with Coomassie Brilliant Blue as in [40]. More than 10 mg purified VNUT can be obtained from 1 L of E. coli culture. b Substrate specificities of SLC17 members. The SLC17 family comprises Cl⁻-activated anion transporters and has nine members. The SLC17A1–4 encode polyspecific anion exporters and prefer urate or hippuric acid as a substrate. The SLC17A5 protein possesses at least three distinct transporter functions: Na⁺/phosphate co-transport, H⁺/sialic acid antiport, and Δψ-driven aspartate and glutamate transport. SLC17A6–8 (VGLUT1, VGLUT2, and VGLUT3) are polyspecific in nature and recognize various glutamate analogues, preferring cyclic glutamate analogues including 1-aminocyclohexane-trans-1, 3-dicarboxylic acid as a substrate, but do not transport aspartate [38]. VNUT is polyspecific and recognizes various nucleotides as substrates. However, the substrate recognition ability is limited to nucleotides and no activity is found for the substrates of other members. Likewise, other SLC17 family members do not transport nucleotides [4]. For details, see ref. [4]