Identification of a Gene Essential for the First Committed Step in the Biosynthesis of Bacteriochlorophyll c

Abstract

Bacteriochlorophylls (BChls) c, d, and e are the major chlorophylls in chlorosomes, which are the largest and one of the most efficient antennae produced by chlorophototrophic organisms. In the biosynthesis of these three BChls, a C-13 2 -methylcarboxyl group found in all other chlorophylls (Chls) must be removed. This reaction is postulated to be the first committed step in the synthesis of these BChls. Analyses of gene neighborhoods of (B)Chl biosynthesis genes and distribution patterns in organisms producing chlorosomes helped to identify a gene (bciC) that appeared to be a good candidate to produce the enzyme involved in this biochemical reaction. To confirm that this was the case, a deletion mutant of an open reading frame orthologous to bciC, CT1077, was constructed in Chlorobaculum tepidum, a genetically tractible green sulfur bacterium. The CT1077 deletion mutant was unable to synthesize BChl c but still synthesized BChl a and Chl a. The deletion mutant accumulated large amounts of various (bacterio)pheophorbides, all of which still had C-13 2 -methylcarboxyl groups. A C. tepidum strain in which CT1077 was replaced by an orthologous gene, Cabther_B0031 from "Candidatus Chloracidobacterium thermophilum" was constructed. Although the product of Cabther_B0031 was only 28% identical to the product of CT1077, this strain synthesized BChl c, BChl a, and Chl a in amounts similar to wild-type C. tepidum cells. To indicate their roles in the first committed step of BChl c, d, and e biosynthesis, open reading frames CT1077 and Cabther_B0031 have been redesignated bciC. The potential mechanism by which BciC removes the C-13 2 -methylcarboxyl moiety of chlorophyllide a is discussed.

Advances in the members and biosynthesis of chlorophyll family

“…c, d, e, and f: In the biosynthesis of BChl c, d, e, and f, the C13 2 -methoxycarbonyl group is removed by the BciC enzyme first. After the C-13 2 -methoxycarbonyl group of Chlide a is removed by the BciC enzyme, 3-vinyl-bacteriochlorophyllide d (3V-BChlide d) is formed (Liu andBryant 2011, Teramura et al 2016a). Then, the BchF or BchV enzyme hydrates the C-3 vinyl group to introduce the C-3 1 -hydroxyl group to form BChlide d , Teramura et al 2016b.…”

BciC‐Catalyzed C132‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

“…The introduction of the 3 1 ‐hydroxy group is based on the hydration of the vinyl group to the 1‐hydroxyethyl group at the C3‐position by hydratases BchF and BchV . It has been reported that a BciC enzyme catalyzed the removal of a methoxycarbonyl group at the C13 2 ‐position, which reduced steric hindrance around the 13‐ketocarbonyl group . These chemical modifications provide more interactive 3 1 ‐hydroxy and 13‐carbonyl groups.…”

“…The genome sequence analysis of this bacterium has already been completed, and parts of the biosynthetic pathways of BChl c have been revealed by genetic studies . Liu and Bryant first reported that a bciC gene affected removal of the C13 2 ‐methoxycarbonyl group in the biosynthesis of BChl c . Later, we examined the in vitro BciC enzymatic reaction, and revealed that the BciC enzyme catalyzed demethoxycarbonylation of chlorophyllide a (Chlide a ) to pyrochlorophyllide a (pyroChlide a ; Figure ) .…”

Specific Gene bciD for C7-Methyl Oxidation in Bacteriochlorophyll e Biosynthesis of Brown-Colored Green Sulfur Bacteria

“…tepidum , a genetically tractable model organism of GSB [8], [9]. Following the recent discovery of an enzyme for removal of the 13 2 -methoxycarbonyl group from Chlide a , called BciC [10], all the genes encoding BChls c and d biosynthetic enzymes were revealed. However, only one step in the biosynthesis of BChl e has been unidentified, i.e., an enzyme producing a formyl group at the C7 position of bacteriochlorophyllide (BChlide) e (Fig.…”