Identification of the cysteine residue responsible for oxidative inactivation of mouse galectin-2.

Galectins are a group of animal lectins characterized by their specificity for β-galactosides. Mouse galectin-2 (mGal-2) is predominantly expressed in the gastrointestinal tract and has been identified as one of the main gastric mucosal proteins that are uniquely sensitive to S-nitrosylation. We have previously reported that oxidation of mGal-2 by hydrogen peroxide (H ₂ O ₂ ) resulted in the loss of sugar-binding ability, whereas pre-treatment of mGal-2 with S-nitrosocysteine prevented H ₂ O ₂ -induced inactivation. In this study, we used point-mutated recombinant mGal-2 proteins to study which of the two highly conserved Cys residues in mGal-2 must be S-nitrosylated for protection against oxidative inactivation. Mutation of Cys ⁵⁷ to a Met residue (C57M) did not result in lectin inactivation following H ₂ O ₂ treatment, whereas Cys ⁷⁵ mutation to Ser (C75S) led to significantly reduced lectin activity, as is the case for wild-type mGal-2. However, pre-treatment of the C75S mutant with S-nitrosocysteine protected the protein from H ₂ O ₂ -induced inactivation. Therefore, Cys ⁵⁷ is suggested to be responsible for oxidative inactivation of the mGal-2 protein, and protection of the sulfhydryl group of the Cys ⁵⁷ in mGal-2 by S-nitrosylation is likely important for maintaining mGal-2 protein function in an oxidative environment such as the gastrointestinal tract.
(© The Authors 2016. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.)