Structural mechanisms for the S-nitrosylation-derived protection of mouse galectin-2 from oxidation-induced inactivation revealed by NMR.

Galectin-2 (Gal-2) is a lectin thought to play protective roles in the gastrointestinal tract. Oxidation of mouse Gal-2 (mGal-2) by hydrogen peroxide (H2O2) results in the loss of sugar-binding activity, whereas S-nitrosylation of mGal-2, which does not change its sugar-binding profile, has been shown to protect the protein from H2O2-induced inactivation. One of the two cysteine residues, C57, has been identified as being responsible for controlling H2O2-induced inactivation; however, the underlying molecular mechanism has not been elucidated. We performed structural analyses of mGal-2 using nuclear magnetic resonance (NMR) and found that residues near C57 experienced significant chemical shift changes following S-nitrosylation, and that S-nitrosylation slowed the H2O2-induced aggregation of mGal-2. We also revealed that S-nitrosylation improves the thermal stability of mGal-2 and that the solvent accessibility and/or local dynamics of residues near C57 and the local dynamics of the core-forming residues in mGal-2 are reduced by S-nitrosylation. Structural models of Gal-2 indicated that C57 is located in a hydrophobic pocket that can be plugged by S-nitrosylation, which was supported by the NMR experiments. Based on these results, we propose two structural mechanisms by which S-nitrosylation protects mGal-2 from H2O2-induced aggregation without changing its sugar-binding profile: (a) stabilization of the hydrophobic pocket around C57 that prevents oxidation-induced destabilization of the pocket, and (b) prevention of oxidation of C57 during the transiently unfolded state of the protein, in which the residue is exposed to H2O2. DatabaseNuclear magnetic resonance assignments for non-S-nitrosylated mGal-2 and S-nitrosylated mGal-2 have been deposited in the BioMagResBank () under ID code 27237 for non-S-nitrosylated mGal-2 and ID code 27238 for S-nitrosylated mGal-2.