title: In vitro stereospecific hydration activities of the 3-vinyl group of chlorophyll derivatives by BchF and BchV enzymes involved in bacteriochlorophyll c biosynthesis of green sulfur bacteria.
abstract: The photosynthetic green sulfur bacterium Chlorobaculum (Cba.) tepidum produces bacteriochlorophyll (BChl) c pigments bearing a chiral 1-hydroxyethyl group at the 3-position, which self-aggregate to construct main light-harvesting antenna complexes, chlorosomes. The secondary alcoholic hydroxy group is requisite for chlorosomal aggregation and biosynthesized by hydrating the 3-vinyl group of their precursors. Using recombinant proteins of Cba. tepidum BchF and BchV, we examined in vitro enzymatic hydration of some 3-vinyl-chlorophyll derivatives. Both the enzymes catalyzed stereoselective hydration of zinc 3-vinyl-8-ethyl-12-methyl-bacteriopheophorbide c or d to the zinc 31R-bacteriopheophorbide c or d homolog, respectively, with a slight amount of the 31S-epimric species. A similar R-stereoselectivity was observed in the BchF-hydration of zinc 3-vinyl-8-ethyl- and propyl-12-ethyl-bacteriopheophorbides c, while their BchV-hydration gave a relatively larger amount of the 31S-epimers. The in vitro stereoselective hydration confirmed the in vivo production of the S-epimeric species by BchV. The enzymatic hydration for the above 8-propylated substrate proceeded more slowly than that for the 8-ethylated, and the 8-isobutylated substrate was no longer hydrated. Based on these results, biosynthetic pathways of BChl c homologs and epimers are proposed.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
authors.forename: Misato
authors.initials: M
authors.lastname: Teramura
authors.affiliation: Department of Medical Biochemistry, Kurume University School of Medicine, Kurume, Fukuoka, 830-0011, Japan.
authors.forename: Jiro
authors.initials: J
authors.lastname: Harada
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan. tamiaki@fc.ritsumei.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000096:biosynthesis* / Q000737:chemistry; D053898:Biosynthetic Pathways; D019414:Chlorobi / Q000201:enzymology / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D066298:In Vitro Techniques; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; C002084:bacteriochlorophyll c
keywords: Chlorobaculum tepidum; Chlorophyll; Chlorosome; Epimer; Homolog; Hydratase
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