2.A.27.1.6
Na²⁺:glutamate symporter, GltS, of 401 aas and 12 TMSs in a 6 + 6 TMS arrangement, functioning with a periplasmic L-glutamate binding protein (Jaques et al. 2025).  BP0403 binds L-glutamate with nanomolar affinity. Genome context analysis of BP0403 reveals no TRAP membrane component genes; instead, it co-localizes with translational coupling with gltS, encoding a Na⁺/glutamate symporter. In other bacteria, fused BP0403-GltS homologues, strongly suggesting that this constitutes a completely novel SBP-dependent secondary active transporter. Structural comparisons suggest GltS operates by an elevator-type mechanism, like TRAP transporters; the association of an SBP with this class of secondary transporter is a novel theme (Jaques et al. 2025).