2.A.56.1.3
Na⁺-dependent (smf-driven) sialic acid (N-acetyl neuraminic acid) transporter, SiaTP (Allen et al., 2005; Severi et al., 2005; Johnston et al., 2008). SiaT is also called SiaQM (Mulligan et al., 2009).  Also transports the related sialic acids, N-glycolylneuraminic acid (Neu5Gc) and 3-keto-3-deoxy-D-glycero-D-galactonononic acid (KDN) (Hopkins et al. 2013). Peter et al. 2024 have proposed that conformational coupling of the sialic acid TRAP transporter HiSiaQM with its substrate binding protein HiSiaP accounts for its energetic features. The SBP can adopt an open- or closed state depending on the presence of substrate. The two transmembrane domains of TRAP transporters form a monomeric elevator whose function is strictly dependent on the presence of a sodium ion gradient (Peter et al. 2024).  cryo-EM structure of the Haemophilus influenzae N-acetylneuraminate TRAP transporter (HiSiaQM) at 2.99 Å resolution (extending to 2.2 Å at the core), revealed new features (Currie et al. 2024). A hydrophobic surface pocket of the SBP is crucial for the allosteric mechanism and for the conformational rearrangement that occurs upon binding of sialic acid to the SBP (Schneberger et al. 2024). Conformational coupling of the sialic acid TRAP transporter SiaQM (SaiT) with its substrate binding protein SiaP has been demonstrated (Peter et al. 2024). .