The complex tetrapyrrole biosynthetic pathway is responsible for synthesizing important metabolites such as vitamin B12, hemes, bilins and chlorophylls. The """"""""common trunk"""""""" of the pathway from 5-aminolevulinate to protoporphyrin IX, has received the most attention owing to the fact that a number of heredity diseases (porphyrias) are caused by the overproduction of heme precursors. Clinical manifestations of overproducing these intermediates range from simple skin lesions, to psychotic disorders, to death. The vitamin B12 branch of the pathway has also received considerable attention as of late. Many genes involved in vitamin B12 synthesis have been identified in Pseudomonas dentrificans and in Salmonella typhimurium. In contrast to the information on heme and vitamin B12 synthesis, there is little information on genes which control synthesis of the Mg-tetrapyrrole branch which is responsible for synthesis of chlorophylls and bacteriochlorophylls. In this proposal we plan to perform detailed biochemical and genetic analysis of the Mg-tetrapyrrole biosynthetic pathway from the bacterium Rhodobacter capsulatus. This includes (i) Biochemical characterization of enzymes from the Mg-tetrapyrrole branch of the biosynthetic pathway, (ii) Biochemical and genetic characterization of a redox responding transcription factor that regulates expression of heme, Mg-tetrapyrrole and carotenoid biosynthesis genes as well as polypeptides that comprise the light harvesting-II portion of the photosystem. (iii). Characterization of additional transcriptional and post-transcriptional regulatory factors that controls the flow of intermediates through this branch of the tetrapyrrole biosynthetic pathway. (iv) Investigations on Mg-tetrapyrrole biosynthesis in the cyanobacterium Synechocystis PCC 6803 will also be initiated for use in a comparative analysis as well as a model system for Mg-tetrapyrrole biosynthesis in eukaryotes. A thorough understanding of the tetrapyrrole biosynthetic pathway has some far ranging practical implications beyond an academic philosophical interest. These include some obvious commercial applications, such as the design of herbicides that target enzymes in the Mg tetrapyrrole pathway, and the health implications of overproducing tetrapyrrole endproducts such as vitamin B12 and heme. It should also not be overlooked that tetrapyrrole driven photosynthesis is the primary route of capturing and supplying energy to living cells and, consequently, it is the most important source of energy in our technological world.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM053940-02
Application #
2430493
Study Section
Special Emphasis Panel (ZRG5-MBC-1 (02))
Project Start
1996-06-01
Project End
2000-05-31
Budget Start
1997-06-01
Budget End
1998-05-31
Support Year
2
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Indiana University Bloomington
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
006046700
City
Bloomington
State
IN
Country
United States
Zip Code
47401
Smart, James L; Bauer, Carl E (2006) Tetrapyrrole biosynthesis in Rhodobacter capsulatus is transcriptionally regulated by the heme-binding regulatory protein, HbrL. J Bacteriol 188:1567-76
Swem, Lee R; Gong, Xing; Yu, Chang-An et al. (2006) Identification of a ubiquinone-binding site that affects autophosphorylation of the sensor kinase RegB. J Biol Chem 281:6768-75
Dragnea, Vladimira; Waegele, Matthias; Balascuta, Septimiu et al. (2005) Time-resolved spectroscopic studies of the AppA blue-light receptor BLUF domain from Rhodobacter sphaeroides. Biochemistry 44:15978-85
Anderson, Spencer; Dragnea, Vladimira; Masuda, Shinji et al. (2005) Structure of a novel photoreceptor, the BLUF domain of AppA from Rhodobacter sphaeroides. Biochemistry 44:7998-8005
Swem, Danielle L; Swem, Lee R; Setterdahl, Aaron et al. (2005) Involvement of SenC in assembly of cytochrome c oxidase in Rhodobacter capsulatus. J Bacteriol 187:8081-7
Nomata, Jiro; Swem, Lee R; Bauer, Carl E et al. (2005) Overexpression and characterization of dark-operative protochlorophyllide reductase from Rhodobacter capsulatus. Biochim Biophys Acta 1708:229-37
Smart, James L; Willett, Jonathan W; Bauer, Carl E (2004) Regulation of hem gene expression in Rhodobacter capsulatus by redox and photosystem regulators RegA, CrtJ, FnrL, and AerR. J Mol Biol 342:1171-86
Bauer, Carl; Elsen, Sylvie; Swem, Lee R et al. (2003) Redox and light regulation of gene expression in photosynthetic prokaryotes. Philos Trans R Soc Lond B Biol Sci 358:147-53; discussion 153-4
Swem, Lee R; Kraft, Brian J; Swem, Danielle L et al. (2003) Signal transduction by the global regulator RegB is mediated by a redox-active cysteine. EMBO J 22:4699-708
Kraft, Brian J; Masuda, Shinji; Kikuchi, Jun et al. (2003) Spectroscopic and mutational analysis of the blue-light photoreceptor AppA: a novel photocycle involving flavin stacking with an aromatic amino acid. Biochemistry 42:6726-34

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