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Title: CHARACTERIZATION OF CYTOCHROME CM FROM SYNECHOCYSTIS 6803:OVEREXPRESSION IN E. COLI IN: PHOTOSYNTHESIS: MECHANISMS AND EFFECTS, ED. G. GARAB PP. 1505-1510 KLUWER ACAD. PUBLISHERS THE NETHERLANDS

Author
item CHO, Y S - PLANT BIOLOGY UOFI URBANA
item PAKRASI, H B - WASHINGTON UNIVERSITY STL
item WHITMARSH, CLIFFORD

Submitted to: Photosynthesis Mechanism and Effects
Publication Type: Proceedings
Publication Acceptance Date: 10/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Photosynthesis provides the energy and building blocks for plant growth and productivity. The photosynthetic process is made up of a series of molecular reactions that convert light energy into chemical energy and carbon dioxide into carbohydrates. To improve photosynthetic performance we need to understand the function and structure of the proteins that together make up the photosynthetic apparatus. With this knowledge, molecular genetics opens the way to manipulate photosynthesis for optimization under diverse environmental conditions. With this aim we have introduced the gene for a metal containing protein from a photosynthetic organism into the bacterium E. Coli. We showed that the gene was expressed, producing a heme-containing protein that had never been seen before. We characterized the physical properties of the protein and will attempt to determine its three-dimensional structure. This information will allow us to discover its role in photosynthesis, with the goal of improving photosynthetic performance.

Technical Abstract: Three c-type cytochromes have been isolated from the cyanobacterium Synechocystis 6803:cytochrome f, cytochrome c6 and cytochrome c550. Based on genetic analysis an additional c-type cytochrome, cytochrome cM, has been identified. The predicted protein consists of 105 amino acids with a characteristic heme-binding motif. The first 24 amino acids of the N-terminal create a hydrophobic tail that is proposed to act as either a transit sequence or a membrane anchor, indicating the expressed protein would be located in the thylakoid lumen. Here we report the first isolation of cytochrome cM. We overexpressed the soluble portion cytochrome cM in E. Coli. Using a poly-His tag, the protein has been purified and characterized. The N-terminal amino acid sequence confirms that the overexpressed protein is cytochrome cM. The isolated protein binds heme and has an absorption peak in the Soret-band at 414 nm and an alpha-band peak near 551 nm. Potentiometric titrations indicate that the midpoint potential of cytochrome cM lies between 150 and 210 nV (pH7). Our data indicate that cytochrome cM can serve as an electron carrier between cytochrome f and photosystem I.