氧化葡糖杆菌具有丰富的PQQ依赖的膜结合的脱氢酶，能区域专一性的将多元醇的第2位或倒数第2位羟基脱氢氧化，生成相应的2-酮糖（2-ketoses）。只有具备Bertrand-Hudson法则构型的多元醇底物才能被膜结合的脱氢酶催化。而D-半乳糖醇不具有Bertrand-Hudson法则的构型，理论上不能被氧化葡糖杆菌膜结合的脱氢酶脱氢氧化。然而我们的研究发现，该菌不但能催化D-半乳糖醇，而且是区域专一性的将第3位羟基氧化，生成一种新的3位酮糖（3-ketose），并证实该酶是PQQ依赖的与膜结合的GOX1857脱氢酶。本项目拟在此基础上结合生物化学和结构生物学的研究手段深入研究该酶区域专一性地催化半乳糖醇第3位羟基脱氢氧化的分子机理，进而对该酶进行理性设计改造，拓展它的底物范围，来制备其它稀有3-ketoses及其衍生物，为化学药物（如糖苷类药物）的合成提供稀有糖基供体。

Gluconobacter oxydans is one of the most important organisms in industry biotechnology because of its ability to incompletely oxidize various sugars, sugar alcohols and sugar acids, in which those reactions are catalyzed by PQQ-dependent membrane-bound dehydrogenases linked to the respiratory chain. Those PQQ-dependent membrane-bound catalyses the regioselective oxidation of substrates according to the Bertrand-Hudson rule, which states that polyols with a cis arrangement of two secondary hydroxyl groups in D-configuration to the primary alcohol group (D-erythro configuration) are oxidized to the corresponding ketoses. Those polyols without D-erythro configuration can not be oxidized. D-galactitol does not have the D-erythro configuration, and theoretically can not be oxidized by those PQQ-dependent membrane-bound dehydrogenases. Interestingly, we found that G.oxydans can regioselectively oxidize D-galactitol to never reported product 3-ketose D-lyxo-3-hexulose, instead of 2-ketose. Our preliminary studies showed the enzyme regioselectively oxidized D-galactitol to 3-ketose is a kind of PQQ-dependent menbrane-bound dehydrogenase, which does not meet the Bertrand-Hudson rule. Based on such unique reaction, we intend to solve the following key scientific questions: One is to identify the enzyme which biocatalyze the unique reaction and its kenetic constants; the second is to clarify the catalytic mechanism, which could propose a new reaction mechanism of regioselective oxidation of polyols, as well as the addition of new family of PQQ-dependent membrane-bound polyol dehydrogenase, and open the new pathway to biosynthesize 3-ketose.