title: Human serine racemase is allosterically modulated by NADH and reduced nicotinamide derivatives.
abstract: Serine racemase catalyzes both the synthesis and the degradation of d-serine, an obligatory co-agonist of the glutamatergic NMDA receptors. It is allosterically controlled by adenosine triphosphate (ATP), which increases its activity around 7-fold through a co-operative binding mechanism. Serine racemase has been proposed as a drug target for the treatment of several neuropathologies but, so far, the search has been directed only toward the active site, with the identification of a few, low-affinity inhibitors. Following the recent observation that nicotinamide adenine dinucleotide (reduced form) (NADH) inhibits serine racemase, here we show that the inhibition is partial, with an IC50of 246 ± 63 μM, several-fold higher than NADH intracellular concentrations. At saturating concentrations of NADH, ATP binds with a 2-fold lower affinity and without co-operativity, suggesting ligand competition. NADH also reduces the weak activity of human serine racemase in the absence of ATP, indicating an additional ATP-independent inhibition mechanism. By dissecting the NADH molecule, we discovered that the inhibitory determinant is the N-substituted 1,4-dihydronicotinamide ring. Particularly, the NADH precursor 1,4-dihydronicotinamide mononucleotide exhibited a partial mixed-type inhibition, with a KIof 18 ± 7 μM. Docking simulations suggested that all 1,4-dihydronicotinamide derivatives bind at the interdimeric interface, with the ring positioned in an unoccupied site next to the ATP-binding site. This newly recognized allosteric site might be exploited for the design of high-affinity serine racemase effectors to finely modulate d-serine homeostasis.
authors: Department of Pharmacy, University of Parma, Parma, Italy.
authors: Stefano
authors: S
authors: Bruno
authors: Department of Pharmacy, University of Parma, Parma, Italy.
authors: Francesco
authors: F
authors: Marchesani
authors: Department of Food Science, University of Parma, Parma, Italy.
authors: Luca
authors: L
authors: Dellafiora
authors: Department of Pharmacy, University of Parma, Parma, Italy.
authors: Marilena
authors: M
authors: Margiotta
authors: Department of Pharmacy, University of Parma, Parma, Italy.
authors: Serena
authors: S
authors: Faggiano
authors: Department of Pharmacy, University of Parma, Parma, Italy.
authors: Barbara
authors: B
authors: Campanini
authors: Department of Pharmacy, University of Parma, Parma, Italy Institute of Biophysics, CNR, Pisa, Italy National Institute of Biostructures and Biomolecules, Rome, Italy.
authors: Andrea
authors: A
authors: Mozzarelli
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000495:Allosteric Site; D001665:Binding Sites; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D009243:NAD / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism; D009536:Niacinamide / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019998:Racemases and Epimerases / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D000099300:Serine Racemase
chemical_list: D000255:Adenosine Triphosphate; D009243:NAD; D009249:NADP; D009536:Niacinamide; D019998:Racemases and Epimerases; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D000099300:Serine Racemase; C015145:dihydronicotinamide
keywords: NADH; NMDAR; allosteric modulation; nicotinamide; serine racemase