title: ATP binding to human serine racemase is cooperative and modulated by glycine.
abstract: The N-methyl D-aspartate (NMDA) receptors play a key role in excitatory neurotransmission, and control learning, memory and synaptic plasticity. Their activity is modulated by the agonist glutamate and by the co-agonists d-serine and glycine. In the human brain, d-serine is synthesized from l-serine by the dimeric pyridoxal 5'-phosphate-dependent enzyme serine racemase, which also degrades l- and d-serine to pyruvate and ammonia. The dependence of l- and d-serine β-elimination and l-serine racemization activities on ATP concentration was characterized, and was found to be strongly cooperative, with Hill coefficients close to 2 and apparent ATP dissociation constants ranging from 0.22 to 0.41 mm. ATP binding to the holo-enzyme, monitored by the fluorescence changes of the coenzyme, was also determined to be cooperative, with an apparent dissociation constant of 0.24 mm. Glycine, an active-site ligand, increased the serine racemase affinity for ATP by ~ 22-fold, abolishing cooperativity. Conversely, ATP increased the non-cooperative glycine binding 15-fold. These results indicate cross-talk between allosteric and active sites, leading to the stabilization of two alternative protein conformations with ATP affinities of ~ 10 μM and 1.8 mm, as evaluated within the Monod, Wyman and Changeux model. Therefore, intracellular ATP and glycine control d-serine homeostasis, and, indirectly, NMDA receptor activity. Because hyper- and hypo-activation of NMDA receptors are associated with neuropathologies, the development of allosteric drugs modulating serine racemase activity is a promising therapeutic strategy.
authors.affiliation: Department of Life Sciences, University of Parma, Italy.
authors.forename: Marialaura
authors.initials: M
authors.lastname: Marchetti
authors.forename: Stefano
authors.initials: S
authors.lastname: Bruno
authors.forename: Barbara
authors.initials: B
authors.lastname: Campanini
authors.forename: Alessio
authors.initials: A
authors.lastname: Peracchi
authors.forename: Nicole
authors.initials: N
authors.lastname: Mai
authors.forename: Andrea
authors.initials: A
authors.lastname: Mozzarelli
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000495:Allosteric Site; D020134:Catalytic Domain; D004795:Enzyme Stability; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D011487:Protein Conformation; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D000099300:Serine Racemase
chemical_list: D000255:Adenosine Triphosphate; D005998:Glycine; D008024:Ligands; D019998:Racemases and Epimerases; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D000099300:Serine Racemase
keywords: ATP; NMDA receptor; PLP; allostery; cooperativity; d-serine; enzyme regulation; fluorescence; neuropathologies; serine racemase