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

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• 作者：Misato Teramura ; Jiro Harada ; Hitoshi Tamiaki
• 关键词：Chlorobaculum tepidum ; Chlorophyll ; Chlorosome ; Epimer ; Homolog ; Hydratase
• 刊名：Photosynthesis Research
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：130
• 期：1-3
• 页码：33-45
• 全文大小：895 KB
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Life Sciences
  Plant Physiology
  
• 出版者：Springer Netherlands
• ISSN：1573-5079
• 卷排序：130

文摘

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.