Download Protein composition and phosphorylation of diatom thylakoid

Protein composition and phosphorylation of diatom thylakoid membranes
Irina Grouneva
University of Turku, Department of Biochemistry and Food Chemistry
Introduction
Methods
Diatoms are eukaryotic unicellular
photosynthetic algae that play a major
role for the primary production of the
oceans. They dominate turbulent waters
and can survive long dark periods. They
originated in a secondary endosymbiotic
event and possess four plastid
membranes.
- Comparison between the two diatom species, Phaeodactylum
tricornutum and Thalassiosira pseudonana, which genome has been
sequenced
- Treatment of cells with low light, high light or long dark periods
- Thylakoid membrane isolation
- 2D gel electrophoresis
T. pseudonana
-ProQ staining
- Mass
spectrometry
- Identification
of (phospho~)
proteins
Armbrust et al.
2007
Protein phosphorylation is
part of a flexible and rapid
signal transduction in cells in
answer to changes in the
environment, especially light.
So far, there are no extensive
studies of the protein
phosphorylation pattern of
diatom thylakoids.
Aro et al. 2004
- Comparison with data on higher plants
Vener 2007
Genetic background of alternative electron transport in diatoms
There is physiological evidence for the existence of a plastid NAD(P)H
dehydrogenase complex (NDH) in diatoms. Alternative plastoquinone
reduction is one clear indication for PS II-independent electron flow.
No ndh genes are encoded in the plastid of T. pseudonana, but a few
nucleus-encoded proteins show sequence similarity to nhdK and ndhI.
*
One putative protein with a plastid target signal (A S A F A P)* from
T. pseudonana shows sequence similarity to 1) NDC1, 2) one NDH with
double targeting to the chloroplast and the mitochondrion from
Arabidopsis as well as 3) type II NDHs from Chlamydomonas reinhardtii.
A. thaliana P. tricornutum
T. pseudonana
Highly conserved IMMUTANS- and PTOX (plastid terminal oxidase)like proteins are found in the two diatom species. One such protein in
T. pseudonana possesses a plastid target sequence (S A A F A P)**.
putative orthologs
diatom proteins
**
Methodical difficulties
Diatom thylakoid lamellae are organised in stacks of three. Isolation of intact plastids and thylakoid membranes
poses a serious problem for diatom studies. One reason is the difficulty of disrupting the silica shells (frustules)
of the cells without causing a rupture of the chloroplasts. This problem is enhanced by the close interaction of
plastids with membranes of other cell compartments.
Wittpoth et al. 1998
Main goals of project
There is still little information on the signalling pathways in the chloroplasts of diatoms. This project has a twofold goal: 1) to
obtain a general overview of the thylakoid protein composition with a special emphasis on the search for components of
alternative electron transport and 2) to identify phosphoproteins involved in signalling in response to changes in irradiance. The
findings will be put in perspective by a careful comparison to plants and green algae. This work should contribute to the
understanding of signalling on a structural level as well as to the knowledge on diatom biology as a whole.
References: Armbrust et al. 2004 Science 306: 79-86, Aro Suorsa Rokka Allahverdiyeva Paakkarinen Saleem Battchikova Rintamäki 2004 Journal of Experimental Botany 56: 347-356,
Vener 2007 Biochimica et Biophysica Acta 1767: 449-457, Wittpoth Kroth Weyrauch Kowallik Strotmann 1998 Planta 206: 79-85