Chloroplasts structural proteins

Knaff, D. B., 1991. Regnlatory phosphoryladon of chloroplast antenna proteins. Trends in Biochemical Sciences 16 82-83. Additional discussion of the structure of light-harvesdng antenna complexes associated widi photo-synthedc reaction centers can be found in Trends in Biochemical Sciences 11 414 (1986), 14 72 (1989), and 16 181 (1991). 

Therefore, although the function of the helix-loop insertion in mitochondrial Rieske proteins appears to be the same as that of the C-terminal extension in chloroplast Rieske proteins, both structures show no structural similarity or sequence homology. 

Carrell, C. J., Zhang, H., Cramer, W. A., and Smith, J. L., 1997, Biological identity and diversity in photosynthesis and respiration structure of the lumen-side domain of the chloroplast Rieske protein. Structure 5 1613nl625. 

Simeonova, E., van Hasselt, P.R., Dobrucki, J. and Mostowska, A. (2005) Light-dependent reversal of dark-chilling induced changes in chloroplast structure and arrangement of chlorophyll-protein complexes in bean thylakoid membranes. Biochim. Biophys. Acta, 1710, 13-23. 

CJ Carrell, H Zhang, WA Cramer and JL Smith (1997) Biological identity and diversity in photosynthesis and respiration structure of the lumen-side domain of the chloroplast Rieske protein. Structure 5 1613-1625 SE Martinez, D Huang, A Szczepaniak, WA Cramer and JL Smith (1994) Crystal structure of chloroplast cytochrome f reveals a novel cytochrome fold and unexpected heme ligation. Structure 2 95-102 SE Martinez, D Huang, M Ponomarev, WA Cramer and JL Smith (1994) The heme redox center of chloroplast cytochrome f is linked to buried five-water chain. Protein Sci 5 1081-1092... 

As we discuss In Chapter 8, the structure of chloroplasts is similar In many respects to that of mitochondria. Like mitochondria, chloroplasts contain multiple copies of the organellar DNA and ribosomes, which synthesize some chloroplast-encoded proteins using the standard genetic code. Other chloroplast proteins are fabricated on c3rt osolIc ribosomes and are incorporated into the organelle after translation (Chapter 16). 

In this paper, we have summarized our current understanding of the biochemical nature of the triazine binding site within the PS II complex. Studies using the proteolytic enzyme trypsin as a selective, surface-specific modifier of membrane polypeptides and the use of a photoaffinity triazine have been utilized separately to identify the triazine receptor protein as a 32-34 kilodalton (kDal) polypeptide of the PS II complex in peas (Pisum sativum L.). The nature of the covalent attachment of the photoaffinity probe has also enabled us to identify the triazine receptor protein as a product of chloroplast-directed protein synthesis this implies that the structural gene for the triazine receptor polypeptide is encoded on chloroplast DNA. 

A lipoprotein is a biochemical assembly that contains both proteins and lipids. The lipids or their derivatives may be covalently or noncovalently bound to the proteins. Many enzymes, transporters, structural proteins, antigens, adhesins, and toxins are lipoproteins. Examples include the high density and low density lipoproteins of the blood, the transmembrane proteins of the mitochondrion and the chloroplast, and bacterial lipoproteins [34]. Lipoproteins in the blood, an aqueous medium, carry fats around the body. The protein particles have hydrophilic groups aimed outward so as to attract water molecules this makes them soluble in the salt water based blood pool. Triglyceride-fats and cholesterol are carried internally, shielded from the water by the protein particle [35]. 

Jasmonic acid treatment has been reported to result in the inhibition of Hill reaction activity and flash-Oj evolution [73], alteration of intra-chloroplast structure [74] and chlorophyll fluorescence parameters [75], a change in the polypeptide pattern of thylakoid membrane proteins [76] and ultimately a decreased photosynthetic rate [77]. An increase in the rate of dark respiration, photorespiration and stomatal resistance to COj diffusion has also been observed [77,78]. 

Signification of results with isolated mitochondria. The site of incorporation of radioactive amino acids in vitro is almost exclusively insoluble membrane-bound protein (structural protein(s)) while soluble proteins, i.e. those readily lost from mitochondria are unlabelled. A comparable situation is observed with isolated chloroplasts. The comparison of the labelling of the mitochondrial substructures after careful fractionation shows that it is predominantly the inner membrane which is active in protein synthesis. It is concluded that soluble enzymes (cytochrome c, dehydrogenases are easily dissolved) and the outer mitochondrial membranes are synthesized outside of the mitochondria in vivo. 

The genetic analysis of Chlamydomonas chloroplast ribosomal proteins has provided the best authenticated demonstration of the dispersal of genes in two genomes for a complex structure. " The construction of these ribosomes is consequently a manifestation of intergenomic cooperation. 

So here we have, at the very least, strong evidence that the structural gene for a ribosomal component of the chloroplast is located in the nuclear genome (perhaps together, with at least one other which has been identified) and the cistrons for the ribosomal RNA are located in the chloroplast genome (probably together, with at least one gene for a chloroplast ribosomal protein [LC4]). How did this come about ... 

Ji TH, Hess JL and Benson AA (1968) Studies on chloroplast membrane structure. I.Association of pigments with chloroplast lamellar protein, Biochim.Biophys.Acta 150, 676-685. 

An extract from the soluble stromal proteins of purified and intact spinach-leaf chloroplasts was prepared by lysis of the cells in buffer, centrifugation of the suspension of broken cells, and concentration of the supernatant with removal of insoluble material. This extract contained all of the enzymes involved in the condensation of the cyclic moieties of thiamine, thiazole, and pyramine. Thus, the synthesis of thiamine in this extract following the addition of pyramine and putative precursors was a proof that the system had the possibility of building the thiazole. It was found that L-tyrosine was the donor of the C-2 carbon atom of thiazole, as in E. coli. Also, as in E. coli cells, addition of 1 -deoxy-D-f/irco-pen-tulose permitted synthesis of the thiamine structure. The relevant enzymes were localized by gel filtration in a fraction covering the 50- to 350-kDa molecular-mass range. This fraction was able to catalyze the formation of the thiazole moiety of thiamine from 0.1 -mM 1-deoxy-D-t/ireo-pentulose at the rate of 220 pmol per mg of protein per hour, in the presence of ATP and Mg2+. 

Fig. 5. Structural comparison of the water-soluble fragments of the Rieske proteins from (a) spinach chloroplasts and (b) beef heart mitochondria. Conserved smd vEiriable regions are highlighted and the conserved /3-loop discussed in Fig. 6 is denoted by darker gray on the rear of the molecules.

In plants, the photosynthesis reaction takes place in specialized organelles termed chloroplasts. The chloroplasts are bounded in a two-membrane envelope with an additional third internal membrane called thylakoid membrane. This thylakoid membrane is a highly folded structure, which encloses a distinct compartment called thylakoid lumen. The chlorophyll found in chloroplasts is bound to the protein in the thylakoid membrane. The major photosensitive molecules in plants are the chlorophylls chlorophyll a and chlorophyll b. They are coupled through electron transfer chains to other molecules that act as electron carriers. Structures of chlorophyll a, chlorophyll b, and pheophytin a are shown in Figure 7.9. 

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