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Structure investigations of membrane protein OEP16

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Membrane protein structure is continuing to be a topic of interest across the scientific community. However, high resolution structural data of these proteins is difficult to obtain. The amino acid

Membrane protein structure is continuing to be a topic of interest across the scientific community. However, high resolution structural data of these proteins is difficult to obtain. The amino acid transport protein, Outer Envelope Protein, 16kDa (OEP16) is a transmembrane protein channel that allows the passive diffusion of amino acids across the outer chloroplast membrane, and is used as a model protein in order to establish methods that ultimately reveal structural details about membrane proteins using nuclear magnetic resonance (NMR) spectroscopy. Methods include recombinant expression of isotope enriched inclusion bodies, purification and reconstitution in detergent micelles, and pre-characterization techniques including circular dichroism (CD) spectroscopy, dynamic light scattering (DLS), and high pressure liquid chromatography (HPLC). High resolution NMR spectroscopy was able to assign 99% of the amide backbone and the chemical shifts provided detailed secondary structure of OEP16 on a per residue basis using the software TALOS+. Relaxation studies explored the intramolecular dynamics of OEP16 and results strongly support the resonance assignments. Successful titration studies were able to locate residues important for amino acid binding for import into the chloroplast as well as provide information on how the transmembrane helices of OEP16 are packed together. For the first time there is experimental evidence that can assign the location of secondary structure in OEP16 and creates a foundation for a future three dimensional structure.

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Date Created
  • 2012

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Isolation, purification and characterization of photosynthetic membrane proteins from Galdieria sulphuraria and Chlamydomonas reinhardtii

Description

In oxygenic photosynthesis, Photosystem I (PSI) and Photosystem II (PSII) are two transmembrane protein complexes that catalyze the main step of energy conversion; the light induced charge separation that drives

In oxygenic photosynthesis, Photosystem I (PSI) and Photosystem II (PSII) are two transmembrane protein complexes that catalyze the main step of energy conversion; the light induced charge separation that drives an electron transfer reaction across the thylakoid membrane. Current knowledge of the structure of PSI and PSII is based on three structures: PSI and PSII from the thermophilic cyanobacterium Thermosynechococcus elonagatus and the PSI/light harvesting complex I (PSI-LHCI) of the plant, Pisum sativum. To improve the knowledge of these important membrane protein complexes from a wider spectrum of photosynthetic organisms, photosynthetic apparatus of the thermo-acidophilic red alga, Galdieria sulphuraria and the green alga, Chlamydomonas reinhardtii were studied. Galdieria sulphuraria grows in extreme habitats such as hot sulfur springs with pH values from 0 to 4 and temperatures up to 56°C. In this study, both membrane protein complexes, PSI and PSII were isolated from this organism and characterized. Ultra-fast fluorescence spectroscopy and electron microscopy studies of PSI-LHCI supercomplexes illustrate how this organism has adapted to low light environmental conditions by tightly coupling PSI and LHC, which have not been observed in any organism so far. This result highlights the importance of structure-function relationships in different ecosystems. Galdieria sulphuraria PSII was used as a model protein to show the amenability of integral membrane proteins to top-down mass spectrometry. G.sulphuraria PSII has been characterized with unprecedented detail with identification of post translational modification of all the PSII subunits. This study is a technology advancement paving the way for the usage of top-down mass spectrometry for characterization of other large integral membrane proteins. The green alga, Chlamydomonas reinhardtii is widely used as a model for eukaryotic photosynthesis and results from this organism can be extrapolated to other eukaryotes, especially agricultural crops. Structural and functional studies on the PSI-LHCI complex of C.reinhardtii grown under high salt conditions were studied using ultra-fast fluorescence spectroscopy, circular dichroism and MALDI-TOF. Results revealed that pigment-pigment interactions in light harvesting complexes are disrupted and the acceptor side (ferredoxin docking side) is damaged under high salt conditions.

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Date Created
  • 2010