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- Title
Human serine racemase is allosterically modulated by NADH and reduced nicotinamide derivatives.
- Authors
Bruno, Stefano; Marchesani, Francesco; Dellafiora, Luca; Margiotta, Marilena; Faggiano, Serena; Campanini, Barbara; Mozzarelli, Andrea
- 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 cooperative 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 IC50 of 246 177 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 Nsubstituted 1,4-dihydronicotinamide ring. Particularly, the NADH precursor 1,4-dihydronicotinamide mononucleotide exhibited a partial mixed-type inhibition, with a KI of 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 ATPbinding site. This newly recognized allosteric site might be exploited for the design of high-affinity serine racemase effectors to finely modulate D-serine homeostasis.
- Subjects
RACEMASES; ALLOSTERIC regulation; NAD (Coenzyme); AMINO acid synthesis; METHYL aspartate receptors; COOPERATIVE binding (Biochemistry)
- Publication
Biochemical Journal, 2016, Vol 473, Issue 20, p3505
- ISSN
0264-6021
- Publication type
Article
- DOI
10.1042/BCJ20160566