2.A.21.3.1
Glucose or galactose:Na⁺ symporter, SGLT1 (galactose > glucose > fucose). Cotransports water against an osmotic gradient (Naftalin, 2008). SGLT1 harbors a water channel (Barta et al. 2022). TMS IV of the high-affinity sodium-glucose cotransporter participates in sugar binding (Liu et al., 2008) and also participates in the uptake of resveratrol, an anti atherosclerosis polyphenol (Chen et al. 2013).  hSGLT1 is expressed as a disulfide bridged homodimer via C355; a portion of the intracellular 12-13 loop is re-entrant and readily accessible from the extracellular milieu (Sasseville et al. 2016). Possibly, the extracellular loop between TMS 12 and TMS 13 participates in the sugar transport of SGLT1 (Nagata and Hata 2006). SGLT1 also transports water efficiently. Calculation of the unitary water channel permeability, pf, yielded similar values for cell and proteoliposome experiments. The absence of glucose, Na⁺, a membrane potential in vesicles, or the directionality of water flow did not grossly altered the pf. Such a weak dependence on protein conformation indicates that a water-impermeable occluded state (glucose and Na⁺ in their binding pockets) lasts for only a minor fraction of the transport cycle or, alternatively, that occlusion of the substrate does not render the transporter water-impermeable (Erokhova et al. 2016). the ortholog from grass carp (Ctenopharyngodon idellus) of 465 aas and 12 putative TMSs is 80% identical and is found in the anterior and mid intestine (Liang et al. 2020). Sodium-dependent glucose transporter 1 and glucose transporter 2 mediate intestinal transport of quercetrin (Li et al. 2020). Cardiac SGLT1 does not contribute appreciably to overall glucose uptake (Ferté et al. 2021).