Characterization of a group of pyrroloquinoline quinone-dependent dehydrogenases that are involved in the conversion of L-sorbose to 2-Keto-L-gulonic acid in Ketogulonicigenium vulgare WSH-001.

Ketogulonicigenium vulgare WSH-001 is an industrial strain used for vitamin C production. Based on genome sequencing and pathway analysis of the bacterium, some of its potential pyrroloquinoline quinone (PQQ)-dependent dehydrogenases were predicted, including KVU_pmdA_0245, KVU_2142, KVU_2159, KVU_1366, KVU_0203, KVU_0095, and KVU_pmdB_0115. BLAST and function domain searches showed that enzymes encoded by these genes may act as putative PQQ-dependent L-sorbose dehydrogenases (SDH) or L-sorbosone dehydrogenases (SNDH). To validate whether these dehydrogenases are PQQ-dependent or not, these seven putative dehyrogenases were overexpressed in Escherichia coli BL21 (DE3) and purified for characterization. Biochemical and kinetic characterization of the purified proteins have led to the identification of seven enzymes that possess the ability to oxidize L-sorbose or L-sorbosone to varying degrees. In addition, the dehydrogenation of sorbose in K. vulgare is validated to be PQQ dependent, identification of these PQQ-dependent dehydrogenases expanded the PQQ-dependent dehydrogenase family. Besides, the optimal combination of enzymes that could more efficiently catalyze the conversion of sorbose to gulonic acid was proposed. These are important in supporting the development of metabolic engineering strategies and engineering of efficient strains for one-step production of vitamin C in the future.