Human serine racemase is nitrosylated at multiple sites

Publication date: Available online 1 February 2018 Source:Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics Author(s): Francesco Marchesani, Stefano Bruno, Gianluca Paredi, Samanta Raboni, Barbara Campanini, Andrea Mozzarelli Serine racemase is a pyridoxal 5′‑phosphate dependent enzyme responsible for the synthesis of d‑serine, a neuromodulator of the NMDA receptors. Its activity is modulated by several ligands, including ATP, divalent cations and protein interactors. The murine orthologue is inhibited by S-nitrosylation at Cys113, a residue adjacent to the ATP binding site. We found that the time course of inhibition of human serine racemase by S-nitrosylation is markedly biphasic, with a fast phase associated with the reaction of Cys113. Unlike the murine enzyme, two additional cysteine residues, Cys269, unique to the human orthologue, and Cys128 were also recognized as S-nitrosylation sites through mass spectrometry and site-directed mutagenesis. The effect of S-nitrosylation on the fluorescence of tryptophan residues and on that of the pyridoxal phosphate cofactor indicated that S-nitrosylation produces a partial interruption of the cross-talk between the ATP binding site and the active site. Overall, it appears that the inhibition results from a conformational change rather than the direct displacement of ATP.
Source: Biochimica et Biophysica Acta (BBA) Proteins and Proteomics - Category: Biochemistry Source Type: research