Abstract
This thesis deals with the structure and function of two different enzymes, ferrochelatase and magnesium chelatase, that catalyse similar reactions. When this work started, a three-dimensional model of ferrochelatase existed. Much was known about the enzyme, but some details remained unclear. The focus has been to establish where the metal and the porphyrin binds to the enzyme, and how they are put together into one. From experiments performed, binding sites for the two substrates were established. It was found that ferrochelatase binds the porphyrin in a vice like grip and induces a distortion of the ring (paper II). The metal ion has been shown to bind close to the porphyrin (paper V). These findings taken together can provide a model for the catalytic mechanism of the enzyme (paper II and V).
Magnesium chelatase, that consists of three different subunits, was a more open field. With access to a collection of barley mutants, deficient in chlorophyll biosynthesis, some questions regarding magnesium chelatase were intended to be answered. Three barley mutants, that each segregated in three distinguished phenotypes served as a starting point. These mutants were found to be deficient in the smallest subunit (paper I). To further characterise the mutants and how subunits interact, the corresponding mutations were introduced in a bacterial magnesium chelatase (paper IV). A big leap forward came with the three-dimensional structure of the smallest subunit (paper III)
While the data presented in this thesis is converging future research on ferrochelatase to fewer questions, it has done quite the opposite for magnesium chelatase. Thanks to what is presented here, it is now known that the smallest magnesium chelatase subunit belongs to the AAA+ class of ATPases (paper III). Further it has been suggested that the middle sized subunit shows similarities to integrins (paper III), a group of cell surface receptors. The connection between AAA+ proteins and integrins was not previously mentioned, but later similar arrangements have been found in other proteins. However the mechanism of magnesium chelatase is still unknown. Hopefully the new aspects presented here will contribute to reveal its secrets.
Magnesium chelatase, that consists of three different subunits, was a more open field. With access to a collection of barley mutants, deficient in chlorophyll biosynthesis, some questions regarding magnesium chelatase were intended to be answered. Three barley mutants, that each segregated in three distinguished phenotypes served as a starting point. These mutants were found to be deficient in the smallest subunit (paper I). To further characterise the mutants and how subunits interact, the corresponding mutations were introduced in a bacterial magnesium chelatase (paper IV). A big leap forward came with the three-dimensional structure of the smallest subunit (paper III)
While the data presented in this thesis is converging future research on ferrochelatase to fewer questions, it has done quite the opposite for magnesium chelatase. Thanks to what is presented here, it is now known that the smallest magnesium chelatase subunit belongs to the AAA+ class of ATPases (paper III). Further it has been suggested that the middle sized subunit shows similarities to integrins (paper III), a group of cell surface receptors. The connection between AAA+ proteins and integrins was not previously mentioned, but later similar arrangements have been found in other proteins. However the mechanism of magnesium chelatase is still unknown. Hopefully the new aspects presented here will contribute to reveal its secrets.
| Original language | English |
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| Qualification | Doctor |
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| Supervisors/Advisors |
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| Award date | 2002 Dec 13 |
| Publisher | |
| ISBN (Print) | 91-628-5473-9 |
| Publication status | Published - 2002 |
Bibliographical note
Defence detailsDate: 2002-12-13
Time: 13:15
Place: Lecture Hall A, Chemical Centre
External reviewer(s)
Name: O'Brian, Mark
Title: Prof
Affiliation: State University of New York at Buffalo, Department of Biochemistry, Buffalo, NY, U.S.A.
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Article: I. Molecular basis for semidominance of missense mutations in the XANTHA-H (42-kDa) subunit of magnesium chelataseHansson, A., Kannangara, C. G., von Wettstein, D. & Hansson, M. (1999). Proc Natl Acad Sci U S A 96, 1744-9
Article: II. Structural and mechanistic basis of porphyrin metallation by ferrochelataseLecerof, D., Fodje, M., Hansson, A., Hansson, M. & Al-Karadaghi, S. (2000). J Mol Biol 297, 221-32
Article: III. Interplay between an AAA module and an integrin I domain may regulate the function of magnesium chelataseFodje, M. N., Hansson, A., Hansson, M., Olsen, J. G., Gough, S., Willows, R. D. & Al-Karadaghi, S. (2001). J Mol Biol 311, 111-22
Article: IV. Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamersHansson, A., Willows, R. D., Roberts, T. D. & Hansson, M. (2002). Proc Natl Acad Sci U S A 99, 13944-9
Article: V. Metal binding to Bacillus subtilis ferrochelatase and interaction between metal sitesLecerof, D., Fodje, M. N., Alvarez León, R., Olsson, U., Hansson, A., Sigfridsson, E., Ryde, U., Hansson, M. & Al-Karadaghi, S. Accepted to publication in J. Biol. Inorg. Chem.
Subject classification (UKÄ)
- Biological Sciences
Free keywords
- tetrapyrrole
- Plant biochemistry
- Växtbiokemi
- MIDAS
- metallation
- magnesium chelatase
- integrin
- heme
- ferrochelatase
- chlorophyll
- barley
- AAA+
- ATPase