Conversion between two cytochalasin B-binding states of the human GLUT1 glucose transporter

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Transport

Background:

• The facilitative glucose transporter GLUT1 is crucial for glucose uptake in human red blood cells.
• GLUT1 exhibits distinct conformational states that influence its interaction with ligands like cytochalasin B.

Purpose of the Study:

• To investigate the two cytochalasin B-binding states of human red blood cell GLUT1.
• To determine factors affecting the binding state of GLUT1 during purification and analysis.

Main Methods:

• Quantitative affinity chromatography using cytochalasin B on biotinylated cells, membrane vesicles, and proteoliposomes.
• Analysis of cytochalasin B binding via Hummel and Dreyer size-exclusion chromatography and ultracentrifugation.
• Investigating GLUT1 states under varying conditions including biotinylation, cytoskeleton depletion, and vesicle entrapment.

Main Results:

• An equilibrium between two GLUT1 cytochalasin B-binding states was observed in biotinylated cells.
• GLUT1 adopted state 2 in free vesicles but shifted to state 1 upon entrapment.
• Purified and reconstituted GLUT1 primarily existed in state 1, which was stable after proteoliposome entrapment.
• State 1 exhibited a slightly higher affinity for cytochalasin B compared to state 2.

Conclusions:

• The cytochalasin B-binding state of GLUT1 is sensitive to experimental conditions such as biotinylation, cytoskeleton association, and matrix interactions.
• These findings provide insights into GLUT1 conformational dynamics and ligand binding during biochemical studies.