Protein translocation into organelles

Knutton, S., Rosenshine, 1., Pallen, M. J., Nisan, 1., Neves, B. C., Bain, S., Wolff, C., Dougan, G., and Frankel, G. (1998). A novel EspA-associated surface organelle of enteropathogenic Escherichia coli involved in protein translocation into epithelial cells. EMBO. 17, 2166-2176. 

Roise, D and Maduke, M. (1994) Import of a Mitochondrial Presequence into P. Denitrificans, FEBS Letters, 337, 9-13 Cavalier-Smith, T. (1987) The Simultaneous Symbiotic Origin of Mitochondria, Chloroplasts and Microbodies, Annals of the New York Academy of Science, 503, 55-71 Cavalier-Smith, T. (1992) The Number of Symbiotic Origins of Organelles, BioSystems, 28, 91-106 Hartl, F Ostermann, J., Guiard, B and Neupert, W. (1987) Successive Translocation into and out of the Mitochondrial Matrix Targeting of Proteins to the Inner Membrane Space by a Bipartite Signal Peptide, Cell, 51,1027-1037. 

For most proteins of the ER, translocation is coupled with protein synthesis. The synthesis of the growing polypeptide from the ribosome docked onto the ER is sufficient to drive the forward movement of the preprotein into the organelle (Fig. 1 Walter andjohnson, 1994 Matlack et al., 1998). However, it was found that some ER-targeted proteins, especially those found in yeast, could be imported into this organelle in a posttranslational fashion. Thus, in such cases the ribosome can play no part in driving preprotein translocation. Indeed an in vitro ER protein import assay has been developed that utilizes fully synthesized preproteins (Hansen et al., 1986 Rothblatt and Meyer, 1986 Waters and Blobel, 1986), and at least one ER-directed preprotein has been shown to be folded in the cytosol before its translocation into the organelle (Paunola et al., 1998). It seems that for yeast, posttranslational import utilizes the same ER Sec61 translocation channel as that employed in the cotranslational system however, additional factors are also recruited to the complex (Fig. 1 Panzer etal., 1995). 

Translocation Into most organelles usually requires the activity of one or more cytosolic proteins. Describe the basic function of three different cytosolic factors required for translocation into the ER, mitochondria, and peroxisomes,... 

Import of a protein into an organelle usually occurs in three stages recognition, translocation, and maturation. 

Fatty acid utilized by muscle may arise from storage triglycerides from either adipose tissue depot or from lipid stores within the muscle itself. Lipolysis of adipose triglyceride in response to hormonal stimulation liberates free fatty acids (see Section 9.6.2) which are transported through the bloodstream to the muscle bound to albumin. Because the enzymes of fatty acid oxidation are located within subcellular organelles (peroxisomes and mitochondria), there is also need for transport of the fatty acid within the muscle cell this is achieved by fatty acid binding proteins (FABPs). Finally, the fatty acid molecules must be translocated across the mitochondrial membranes into the matrix where their catabolism occurs. To achieve this transfer, the fatty acids must first be activated by formation of a coenzyme A derivative, fatty acyl CoA, in a reaction catalysed by acyl CoA synthetase. 

It has recently been reported that Giardia mitosomes, Trichomonas hydrogenosomes and mitochondria share a similar mode of protein targeting and translocation (Dolezal et al. 2005 Regoes et al. 2005). The import of Giardia IscU and ferredoxin into the organelle was shown to be dependent on... 

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