Mapping the Allosteric Communication Network of Aminodeoxychorismate Synthase |
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| Institution: | 1. Institute of Chemical Biology and Fundamental Medicine (ICBFM) SB RAS, 8 Lavrentiev Avenue, Novosibirsk 630090, Russia;2. SABNP, Univ Evry, INSERM U1204, Université Paris-Saclay, 91025 Evry, France;1. Ludwig-Maximilians-Universitaet Muenchen, Mikrobiologie, Großhaderner Str. 2-4, 82152, Martinsried, Germany;2. Technical University of Munich, Physics of Complex Biosystems, James-Franck-Str. 1, 85748 Garching, Germany;3. University of Göttingen, Institute for Microbiology and Genetics, Dept. of General Microbiology, Grisebachstr. 8, 37077 Göttingen, Germany;1. Department of Chemistry and Biochemistry, The City College of New York, NewYork, NY 10031, USA;2. Graduate Program in Biochemistry, The Graduate Center of CUNY, New York, NY 10016, USA;3. Graduate Program in Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA;4. Division of Chemical Biology and Medicinal Chemistry, University of Texas, Austin, TX 78712, USA;5. Graduate Program in Chemistry, The Graduate Center of CUNY, New York, NY 10016, USA;6. Graduate Program in Physics, The Graduate Center of CUNY, New York, NY 10016, USA;1. Nucleic Acids Structure Research Group, University of Dundee, Dundee, United Kingdom;2. Department of Biology, University of Konstanz, 78457 Konstanz, Germany;3. Department of Molecular Physiology and Biological Physics, University of Virginia, 22908 Charlottesville, VA, USA;4. Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA |
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| Abstract: | Allosteric communication between different subunits in metabolic enzyme complexes is of utmost physiological importance but only understood for few systems. We analyzed the structural basis of allostery in aminodeoxychorismate synthase (ADCS), which is a member of the family of glutamine amidotransferases and catalyzes the committed step of the folate biosynthetic pathway. ADCS consists of the synthase subunit PabB and the glutaminase subunit PabA, which is allosterically stimulated by the presence of the PabB substrate chorismate. We first solved the crystal structure of a PabA subunit at 1.9-Å resolution. Based on this structure and the known structure of PabB, we computed an atomic model for the ADCS complex. We then used alanine scanning to test the functional role of 59 conserved residues located between the active sites of PabB and PabA. Steady-state kinetic characterization revealed four branches of a conserved network of mainly charged residues that propagate the signal from chorismate at the PabB active site to the PabA active site. The branches eventually lead to activity-inducing transformations at (i) the oxyanion hole motif, (ii) the catalytic Cys‐His‐Glu triad, and (iii) glutamine binding residues at the PabA active site. We compare our findings with previously postulated activation mechanisms of different glutamine amidotransferases and propose a unifying regulation mechanism for this ubiquitous family of enzymes. |
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