Electrogenic Na+-coupled sugar symporter that actively transports D-mannose or D-fructose at the plasma membrane, with a Na+ to sugar coupling ratio of 1:1. Transporter activity is driven by a transmembrane Na+ electrochemical gradient set by the Na+/K+ pump. Exclusively recognizes sugar substrates having a pyranose ring with an axial hydroxyl group on carbon 2. Has likely evolved to enable renal reabsorption of D-mannose, an important constituent of oligosaccharide chains of glycoproteins. Contributes to dietary D-fructose reabsorption from glomerular filtrate across the brush border of the kidney