|_Re: 초록_9월 30일 세미나_이정국 교수|
Use of chromatophore membrane vesicles from photosynthetic bacteria for the generation of chemical energy in vitro from light
Jeong K. Lee
Department of Life Science, Sogang University, Seoul 121-742, Korea
The chromatophore membrane vesicles (CMVs) were prepared from Synechocystis sp. PCC6803 and Rhodobacter sphaeroides, which have chlorophyll a (Chl a) and bacteriochlorophyll a (Bchl a), respectively, as the major light-harvesting pigments. Chl a absorbs relatively short-wavelength light, whereas Bchl a absorbs long-wavelength light. The CMVs harbor all the components necessary for the photosynthetic (PS) light reaction and they were shown to generate the chemical energy of ATP and NAD(P)H in vitro from light. The sustainability of CMVs were extended by the biosilicification using silaffin R5. The in vitro light reaction with CMVs was used to to produce 1 oxalate from 2 CO2 molecules in a newly reconstituted cycle. It was further applied to the production of resveratrol, nicotinamide mononucleotide and 5-aminolevulinate. Furthermore, my group expanded the light absorption spectrum of R. sphaeroides in order to increase the efficiency of light energy utilization. Chlorophyll synthase (ChlGSyn) of Synechocystis sp. PCC6803 and bacteriochlorophyll synthase (BchG) of R. sphaeroides esterifiy the C20 isoprenoid group to the chlorophyllide a (Chlide a) and bacteriochlorophyllide a (Bchlide a), to form Chl a and Bchl a, respectively. Both enzymes have high degree of substrate specificities. The ChlGSyn is competitively inhibited by Bchlide a, and likewise BchG is inhibited by Chlide a. Thus, the expression of chlGSyn in trans in R. sphaeroides did not lead to the production of Chl a. Recently, we have found that the activities of ChlGplt of plants including Nicotiana tabacum are not affected by Bchlide a. The expression of chlGplt in trans in R. sphaeroides resulted in the production of Chl a in addition to Bchl a. The gene coding for the light-harvesting complex (LHCaR1) of red alga Porphyridium purpureum, which simply harbors Chl a and zeaxanthin, was expressed in R. sphaeroides after the replacement of crtI3 (3-step phytoene desaturase) and crtC (carotenoid 1,2-hyratase) with the crtI4 (4-step phytoene desaturase), crtY (lycopene cyclase) and crtZ (β-carotene hydroxylase) to form zeaxanthin. The LHCaR1 was successfully produced in the recombinant R. sphaeroides. As far as we understand, this is the first report of the production of LHC containing Chl a together with the PS complexes containing Bchl a, which signifies the beginning step to expand light absorption spectrum of the PS organism.