Characterization of a Plant-like Protochlorophyllide a Divinyl Reductase in Green Sulfur Bacteria

Abstract

The green sulfur bacterium Chlorobium tepidum synthesizes three types of (bacterio)chlorophyll ((B)Chl): BChl a P , Chl a PD , and BChl c F . During the synthesis of all three molecules, a C-8 vinyl substituent is reduced to an ethyl group, and in the case of BChl c F , the C-8 2 carbon of this ethyl group is subsequently methylated once or twice by the radical S-adenosylmethionine enzyme BchQ. The C. tepidum genome contains homologs of two genes, bchJ (CT2014) and CT1063, that are highly homologous to genes, bchJ and AT5G18660, and that have been reported to encode C-8 vinyl reductases in Rhodobacter capsulatus and Arabidopsis thaliana, respectively. To determine which gene product actually encodes a C-8 vinyl reductase activity, the bchJ and CT1063 genes were insertionally inactivated in C. tepidum.

slr1923 of Synechocystis sp. PCC6803 Is Essential for Conversion of 3,8-Divinyl(proto)chlorophyll(ide) to 3-Monovinyl(proto)chlorophyll(ide)

“…Chew and Bryant (2007) confirmed the presence of the corresponding enzyme in a green sulfur bacterium, C. tepidum TL3 (CT1063). On the other hand, Nagata et al (2005) could not identify DVR homologues in most cyanobacteria.…”

“…It is also found in the green sulfur bacterium C. tepidum TLS (Chew and Bryant, 2007). However, it was not found in other cyanobacteria.…”

“…Although the structure of the redox center of F 420 is similar to that of flavin, the manner of redox reaction is similar to that of NAD(P) + ; F 420 accepts two electrons and one proton, like NAD(P) + when it is reduced. Taking into account the reports that vinyl reductase is specific to NADPH (Kolossov and Rebeiz, 2001;Nagata et al, 2005;Chew and Bryant, 2007;Ito et al, 2008) and the structural similarity of F 420 to flavin, a flavin-binding site is expected in the Slr1923 protein. The deduced amino acid sequence shows the motif of a 4Fe4S-type iron-sulfur cluster on its N-terminal side (Fig.…”

“…Nagata et al (2005) and Nakanishi et al (2005) independently identified gene AT5G18660 of Arabidopsis as a divinyl reductase (DVR) that has sequence similarity to isoflavone reductase. By investigation of the mutant created by insertional inactivation, Chew and Bryant (2007) demonstrated that CT1063 (bciA), which is an ortholog of the Arabidopsis gene, encodes a C-8 DVR of Chlorobium tepidum TLS. They also concluded that BchJ, which had been reported to be a vinyl reductase (Suzuki and Bauer, 1995), is not the enzyme.…”

Chlorophyllide a Oxidoreductase Works as One of the Divinyl Reductases Specifically Involved in Bacteriochlorophyll a Biosynthesis

“…In an early study using the purple bacterium Rhodobacter capsulatus, the mutational analysis judged that a bchJ gene encodes one of the subunits for DVR (4,11). However, recent investigations have indicated that BchJ is not DVR and would be a scaffold or chaperone protein for an unidentified route among several biosynthetic steps from 8V-PChlide a to BChl a (8,12). In the case of Chl a synthesis, a AT5G18660 gene of the higher plant Arabidopsis thaliana was identified as a DVR gene because the gene mutant accumulated 8-vinyl-Chls (8V-Chls) a and b (13,14); hereafter in this work, this DVR is called planttype DVR.…”