Folate chemotactic receptors in Dictyostelium discoideum I. Ligand-induced conversion between four receptor states |
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| Institution: | 1. State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, China;2. Department of Chemistry, Dalhousie University, Halifax B3H 4R2, Canada;3. Department of Physics and Atmospheric Science, Dalhousie University, Halifax B3H 4R2, Canada;1. Laboratoire Modélisation, Information et Systèmes (MIS), Université de Picardie Jules Verne (UPJV), 14 quai de la Somme, 80000 Amiens, France;2. ESIEE-Amiens, 14 Quai de la Somme, CS 10100, 80082 Amiens cedex 2, France;1. Department of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zurich, Switzerland;2. Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany;3. Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany;4. Electron Microscopy Core Facility, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany;5. Luxendo GmbH, Kurfürsten-Anlage 58, 69115 Heidelberg, Germany;6. Department for Cell Physiology and Metabolism, University of Geneva, 1 rue Michel Servet, 1211 Geneva 4, Switzerland;1. Service de néphrologie, transplantation rénale, dialyse et aphérèses, hôpital Pellegrin, CHU de Bordeaux, place Amélie-Raba-Léon, 33076 Bordeaux cedex, France;2. Unité Inserm U1034, university Bordeaux, Bordeaux, France;3. Service de cardiologie et hypertension artérielle, hôpital de Pau, 4, boulevard Hauterive, 64064 Pau, France;4. Service de cardiologie, hôpital Haut-Lévêque, CHU de Bordeaux, avenue de Magellan, 33604 Pessac cedex, France;5. Unité Inserm, U1026 BioTis, university Bordeaux, Bordeaux, France;6. Fondation de recherche sur l’hypertension artérielle, 12, rue des Colonnes-du-Trône, 75012 Paris, France;1. Microbiology Department, King Saud University and King Khalid University Hospital, College of Medicine, Riyadh, Saudi Arabia;2. Peadiatric Department, Infectious Disease, King Saud University and King Khalid University Hospital, College of Medicine, Riyadh, Saudi Arabia;3. Medical Science, King Saud University and King Khalid University Hospital, College of Medicine, Riyadh, Saudi Arabia |
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| Abstract: | The presence of three distinct populations of folate binding sites on the surface of Dictyostelium discoideum cells has been reported recently. The A sites (consisting of two subtypes) recognize folic acid, 2-deaminofolic acid and methotrexate with equal affinity and appear to be linked to cAMP synthesis. B and C sites (the latter is composed of two interconvertable subtypes; rapidly equilibrating, CF, and more slowly equilibrating, CS) preferentially bind N10-methylfolic acid and folic acid and may both be involved in the chemotactic response (De Wit, R.J.W. and Van Haastert, P.J.M. (1985) Biochim. Biophys. Acta 814, 199–213; De Wit, R.J.W., Bulgakov, R., Pinas, J.E. and Konijn, T.M. (1985) Biochim. Biophys. Acta 814, 214–226). The present study gives two lines of evidence that the B and C sites are interconvertable. (i) Occupancy of the B-sites by N10-methylfolic acid proceeds at a rate identical to that of the association of this ligand to CS at all concentrations tested. This suggests that association to CS and formation of occupied B sites share a common pathway. (ii) After preincubation with ligand, removal of free ligand results in the reappearance of unoccupied CF sites with kinetics identical to the disappearance of occupied B sites. Furthermore, the existence of a third type of C site, which is formed out of CS and may be converted to B, is proposed. This is based on competition studies using folate analogs with a different affinity for CS and B. |
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