Compartmentation of proteins

Okita TW, Rogers JC. Compartmentation of proteins in the endomembrane system of plant cells. Ann Rev Plant Physiol Plant Mol Biol 1996 47 327-350. 

Siegers, K., T. Waldmann, M. R. Leroux, K. Grein, A. Shevchenko, E. Schiebel, and F. U. Hard (1999). Compartmentation of protein folding in vivo Sequestration of nonnative polypeptide by the chaperonin-GimC system. EMBOJ. 18, 75-84. 

Nonallosterlc mechanisms for regulating protein activity Include proteolytic cleavage, which irreversibly converts inactive zymogens into active enzymes, compartmentation of proteins, and signal-Induced modulation of protein synthesis and degradation. 

AKAPs are a diverse family of about 75 scaffolding proteins. They are defined by the presence of a structurally conserved protein kinase A (PKA)-binding domain. AKAPs tether PKA and other signalling proteins to cellular compartments and thereby limit and integrate cellular signalling processes at specific sites. This compartmentalization of signalling by AKAPs contributes to the specificity of a cellular response to a given external stimulus (e.g. a particular hormone or neurotransmitter). 

In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP). However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4 -phosphopan-tetheine (Figure 45-18). The use of one multienzyme functional unit has the advantages of achieving the effect of compartmentalization of the process within the cell without the erection of permeability barriers, and synthesis of all enzymes in the complex is coordinated since it is encoded by a single gene. 

Of the large number of protein interactions that take place in cells, perhaps the vast majority may be described as transient. Most proteins that modify other molecules do so very rapidly and so interact only briefly with their substrates or binding partners (i.e., enzymes). In addition, since proteins within cells are highly compartmentalized, the affinity of most interactions doesn t have to be very great, because each potential binding partner is within short diffusion distances and the relative concentration of molecules within these small volumes is high. 

Eukaryotic cells have evolved a complex, intracellular membrane organization. This organization is partially achieved by compartmentalization of cellular processes within specialized membrane-bounded organelles. Each organelle has a unique protein and lipid composition. This internal membrane system allows cells to perform two essential functions to sort and deliver fully processed membrane proteins, lipids and carbohydrates to specific intracellular compartments, the plasma membrane and the cell exterior, and to uptake macromolecules from the cell exterior (reviewed in [1,2]). Both processes are highly developed in cells of the nervous system, playing critical roles in the function and even survival of neurons and glia. 

Steward, O. and Schuman, E. M. Compartmentalized synthesis and degradation of proteins in neurons. Neuron 40 347-359, 2003. 

Cellular membranes function as selective barriers and integral membrane protein scaffolds. Membranes allow the compartmentalization of cells, and individual organelles within cells, and are critical in energy transduction and cell signaling. In vivo membranes contain hundreds to thousands of lipid types, making characterization of particular lipid-lipid interactions challenging. 

The compartmentation of cubic phases is geometrically not so well defined as in the case of micelles or vesicles. However, several years ago the very interesting observation was made that cubic phases can incorporate proteins up to 50% of their weight (Ericsson et al, 1983). Usually cubic phases also remain transparent after incorporation of proteins, and in fact it has been possible to carry out circular dichroic investigations of enzymes in such systems, (Larsson, 1989 Portmann et al, 1991 Landau and Luisi, 1993), as shown in Figure 9.19, and even to follow spectroscopically the course of enzymatic reactions (Portmann et al, 1991). 

Toxicity of protein Chloroplast compartmentalization minimizes adverse effects of protein May have serious effects in cytoplasm... 

Translocation of protein kinases is a specific process, encompassing at least two mechanisms to decide the location in the cell at which the kinase will become active. In one mechanism, sequence sections of the protein kinase are used as leader sequences for compartmentalization. 

The compartmentalization of energy generation provides a mechanism for the increased efficiency of high energy bond transfer to form the ultimate cellular fuel ATP, and has been the driving force behind the evolution of the mitochondrion. This viewpoint is supported by studies of the mitochondrial proteome, which have demonstrated that proteins of eubacterial origin predominantly... 

The role of GSH in cellular protection (see below) means that if depleted of GSH, the cell is more vulnerable to toxic compounds. However, GSH is compartmentalized, and this compartmentalization exerts an influence on the relationship between GSH depletion or oxidation and injury. The loss of reduced GSH from the cell leaves other thiol groups, such as those in critical proteins, vulnerable to attack with subsequent oxidation, cross-linking, and formation of mixed disulfides or covalent adducts. The sulfydryl groups of proteins seem to be the most susceptible nucleophilic targets for attack, as shown by studies with paracetamol (see chap. 7), and are often crucial to the function of enzymes. Consequently, modification of thiol groups of enzyme proteins, such as by mercury and other heavy metals, often leads to inhibition of the enzyme function. Such enzymes may have critical endogenous roles such as the regulation of ion concentrations, active transport, or mitochondrial metabolism. There is... 

In prokaryotes DNA, RNA, and protein synthesis all take place in the same cellular compartment. In eukaryotes the DNA is compartmentalized in the cell nucleus, and it became clear long before the biochemistry of these three processes was understood that DNA synthesis takes place in the nucleus, whereas the bulk of protein synthesis takes place in the cytoplasm. From these observations on eukaryotes it was self-evident that DNA cannot be directly involved in the synthesis of protein but must somehow transmit its genetic information for protein synthesis to the cytoplasm. Careful experiments with radioactive labels were used to demonstrate that RNA synthesis takes place in the nucleus much of this RNA is degraded rather quickly, but the portion that survives is mostly transferred to the cytoplasm (fig. 28.1). From observations of this kind it became clear that RNA was the prime candidate for the carrier of genetic information for the synthesis of proteins. 

Insel, P. A., Head, B. P., Patel, H. H., Roth, D. M., Bundey, R. A., and Swaney, J. S. (2005b). Compartmentation of G-protein-coupled receptors and their signalling components in lipid rafts and caveolae. Biochem. Soc. Trans. 33, 1131-1134. 

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