Henrik Aronsson

Docent, Förste Forskningsingenjör

Tel: 031-786 4802
E-post: henrik.aronsson@bioenv.gu.se
Fax: 031-786 2560

Undervisningsområde 

Cellfysiologi, Växtmolekylärbiologi

Forskningsområde/aktuella projekt

INTRACELLULAR PROTEIN TARGETING WITH EMPHASIS ON CHLOROPLASTS

The chloroplast protein targeting
Arabidopsis thaliana is an excellent model system for studying chloroplast protein import, and the necessary techniques are well established. Most chloroplast proteins are encoded in the nucleus and imported post-translationally into chloroplasts. A protein complex in the chloroplast envelope, called the translocon, mediates import. Components of the translocon are called Toc or Tic, for translocon at the outer/inner envelope membrane of chloroplasts.
A lot of Toc and Tic components have been identified and characterised, but many of their functions remain to be determined in detail. Proteins imported by the translocon have a transit peptide that targets them to the main receptors Toc33 and Toc159. Thereafter the incoming protein is transferred over the envelope membranes through the Toc75 and Tic110 channels. The transit peptide is removed upon transfer across the envelope membranes. Our major focus has been on Toc64 and Tic55 but work has also been performed with focus on Toc33 and Mgd1.

The chloroplast vesicle transport system
Inside the chloroplast lies the thylakoid membrane. The thylakoid membrane consists of different elements e.g. photosynthetic pigments, hydrophobic proteins and glycerolipids. Newly synthesized lipids are transported to the thylakoid membrane from the envelope. As the inner envelope membrane and the thylakoids are separated by an aqueous stroma, a special transport system is believed to exist. Previous ultrastructural and biochemical studies support a vesicular transfer mode.
Vesicular trafficking in the secretory pathway participates in transport of proteins to their appropriate location, e.g. ER, Golgi and plasma membrane. Proteins are sorted into vesicles that are released from a donor compartment and then transferred to an acceptor compartment by fusion with its membrane. The vesicular traffic is mediated by COPI, COPII and clathrin coated vesicles and coat assembly and vesicle budding are regulated by small GTPases such as ARF and SAR.
Using the Arabidopsis genome and web-based localization prediction tools one can identify putative chloroplast proteins with a high sequence similarity to the components of the cytosolic vesicular trafficking. We recently identified one of these putative components and named it CPSAR1. CPSAR1 has a similar role as SAR in the cytosol i.e. facilitating transport of lipids (and perhaps proteins) from a donor membrane (the envelope) to an acceptor membrane (the thylakoid).

Current members of the group
PhD students
Nadir Zaman Khan
Mohamed Alezzawi
Emelie Lindquist

Postdocs
Dr Sazzad Karim
Dr Reza Amirjani

Publications list, CV, Research field, Group members

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