Title : Membrane topology of the human
Na+/glucose cotransporter
SGLT1
Abstract :
- The membrane topology of the human Na+/glucose cotransporter SGLT1 has been probed using N-glycosylation scanning mutants and nested truncations
- Functional analysis proved essential for establishment of signal-anchor topology
- The resultant model diverges significantly from previously held sup positions of structure based primarily on hydropathy analysis
- SGLT1 incorporates 14 membrane spans
- The N terminus resides extracellularly, and two hydrophobic regions form newly recognized membrane spans 4 and 12; the large charged domain near the C terminus is cytoplasmic
- This model was evaluated further using two advanced empirically-based algorithms predictive of transmembrane helices
- Helix ends were predicted using thermo-dynamically-based algorithms known to predict x-ray crystallographically determined transmembrane helix ends
- Several considerations suggest the hydrophobic C terminus forms a 14th transmembrane helix, differentiating the eukaryotic members of the SGLT1 family from bacterial homologues
- Our data inferentially indicate that these bacterial homologues incorporate 13 spans, with an extracellular N terminus
- The model of SGLT1 secondary structure and the predicted helix ends signify information prerequisite for the rational design of further experiments on structure/function relationships