You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Determinants of regioselectivity and chemoselectivity in fosfomycin resistance protein FosA from QM/MM calculations. FosA is a manganese-dependent enzyme that utilizes a Mn(2+) ion to catalyze the inactivation of the fosfomycin antibiotic by glutathione (GSH) addition. We report a theoretical study on the catalytic mechanism and the factors governing the regioselectivity and chemoselectivity of FosA. Density functional theory (DFT) calculations on the uncatalyzed reaction give high barriers and almost no regioselectivity even when adding two water molecules to assist the proton transfer. According to quantum mechanics/molecular mechanics (QM/MM) calculations on the full solvated protein, the enzyme-catalyzed glutathione addition reaction involves two major chemical steps that both proceed in the sextet state: proton transfer from the GSH thiol group to the Tyr39 anion and nucleophilic attack by the GSH thiolate leading to epoxide ring-opening. The second step is rate-limiting and is facilitated by the presence of the high-spin Mn(2+) ion that functions as a Lewis acid and stabilizes the leaving oxyanion through direct coordination. The barrier for C1 attack is computed to be 8.9 kcal/mol lower than that for C2 attack, in agreement with the experimentally observed regioselectivity of the enzyme. Further QM/MM calculations on the alternative water attack predict a concerted mechanism for this reaction, where the deprotonation of water, nucleophilic attack, and epoxide ring-opening take place via the same transition state. The calculated barrier is 8.3 kcal/mol higher than that for GSH attack, in line with the observed chemoselectivity of the enzyme, which manages to catalyze the addition of GSH in the presence of water molecules around its active site. The catalytic efficiency, regioselectivity, and chemoselectivity of FosA are rationalized in terms of the influence of the active-site protein environment and the different stabilization of the distorted substrates in the relevant transition states.
{"Chemical": ["glutathione", "Lewis acid", "GSH", "GSH thiol", "epoxide", "Mn(2+)", "Tyr", "manganese", "fosfomycin", "GSH thiolate"]}