Structural and Physiologic Determinants of Human Erythrocyte Sugar Transport Regulation by Adenosine Triphosphate

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Abstract
Human erythrocyte sugar transport is mediated by the integral membrane protein GLUT1 and is regulated by cytosolic ATP [Carruthers, A., and Helgerson, A. L. (1989) Biochemistry 28, 8337−8346]. This study asks the following questions. (1) Where is the GLUT1 ATP binding site? (2) Is ATP−GLUT1 interaction sufficient for sugar transport regulation? (3) Is ATP modulation of transport subject to metabolic control? GLUT1 residues 301−364 were identified as one element of the GLUT1 ATP binding domain by peptide mapping and N-terminal sequence analysis of proteolytic fragments of azidoATP-photolabeled GLUT1. Nucleotide binding and sugar transport experiments undertaken with dimeric and tetrameric forms of GLUT1 indicate that only tetrameric GLUT1 binds and is subject to modulation by ATP. Reconstitution experiments indicate that nucleotide and tetrameric GLUT1 are sufficient for ATP modulation of sugar transport. Feedback control of GLUT1 regulation by ATP was investigated by measuring sugar uptake into erythrocyte ghosts containing or lacking ATP and glycolytic intermediates. Only AMP and ADP modulate ATP regulation of transport. Reduced cytosolic pH inhibits ATP modulation of GLUT1-mediated 3OMG uptake and increases Kd(app) for ATP interaction with GLUT1. We conclude that tetrameric but not dimeric GLUT1 is subject to direct regulation by cytosolic ATP and that this regulation is antagonized by intracellular AMP and acidification.

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