Abstract
Light-dependent protochlorophyllide oxidoreductase (LPOR) catalyzes a unique light-driven reaction that produces chlorophyllide a, the direct precursor of chrolophyll a. A mutant (Δpor) lacking por gene encoding LPOR of cyanobacterium Synechocystis sp. PCC 6803 does not grow under aerobic conditions, while it grows under anaerobic conditions. Therefore, the Δpor mutant would be a suitable strain for in-vivo evaluation system for LPOR variants. A marine cyanobacterium Synechococcus sp. CC 9311 possesses three LPOR-like genes in the genome. Two of them are phylogenetically distant from the group containing LPORs from freshwater cyanobacteria and plants. The three genes were individually introduced into the Δpor mutant for expression, and the growth of the resultant transformants was examined under aerobic conditions. In addition, LPOR activity of the purified proteins expressed in E. coli was examined and Km values for protochlorophyllide and NADPH were determined for one of them. We also report a result of a cyanobacterial LPOR variant lacking a loop specific for LPOR examined by the Δpor expression system.
