Role in protein transport

Orci, L., Glick, B. S. and Rothman, J. E. A new type of coated vesicular carrier that appears not to contain clathrin its possible role in protein transport within the Golgi stack. Cell 46 171-184,1986. 

Ubiquitin, found in several cellular compartments (e.g., cytoplasm and the nucleus), belongs to a class of proteins referred to as stress proteins. Stress proteins, also called heat shock proteins (hsp), are so named because their syntheses are accelerated (and in some cases initiated) when cells encounter stress. (The name heat shock protein is misleading, because a variety of stressful conditions besides elevated temperature induce their synthesis.) Other stress proteins act as molecular chaperones, that is, they promote protein folding (p. 692). Heat shock proteins and molecular chaperones also play significant roles in protein transport and intermolecular interactions. 

Nonbilayer phase formation has been found to play an important role in membrane transport, fusion, and exo- and endocytosis [23,27,28]. In addition, the presence of peptides and proteins promotes the formation of nonbilayer phases [29,30], which may be needed to keep them in a functional state [18,31]. 

It should be noted that the dynamics studied by fluorescence methods is the dynamics of relaxation and fluctuations of the electric field. Dipole-orientational processes may be directly related to biological functions of proteins, in particular, charge transfer in biocatalysis and ionic transport. One may postulate that, irrespective of the origin of the charge balance disturbance, the protein molecule responds to these changes in the same way, in accordance with its dynamic properties. If the dynamics of dipolar and charged groups in proteins does play an important role in protein functions, then fluorescence spectroscopy will afford ample opportunities for its direct study. 

Transferrin plays a major role in the transport and cellular uptake of thorium (Peter and Lehmann 1981). Thorium can be displaced from transferrin by an excess of iron, but it is not known whether thorium and iron bind to the same sites on the transferrin molecule. It has also been determined that thorotrast (Th02 colloid) blocks the uptake of labelled protein by the RES in female rabbits and in both male and female rats (Hyman and Paldino 1967). The mechanism of the blockade is not clear. Sex differences were found in rabbits but not in rats. The particle size of the Thorotrast colloid influences its effect on the uptake of protein only particles larger than 1 pm will interfere with uptake of protein by the RES. 

Polyphosphate was chosen as a polyelectrolyte in addition to the erythrocyte ghost protein, because van Steveninck demonstrated (17) that polyphosphate plays an important role in membrane transport in yeast cells. The results obtained with polyphosphate, especially on protein-covered membranes, indicate that the possibility of ionic transport is strongly enhanced. 

In addition to its previously mentioned role in copper transport, ceruloplasmin is an amine oxidase, a superoxide dismutase, and a ferrooxidase able to catalyze the oxidation of Fe2+ to Fe3+. Ceruloplasmin contains three consecutive homologous 350-residue sequences which may have originated from an ancestral copper oxidase gene. Like ascorbate oxidase, this blue protein contains copper of the three different types. Blood clotting factors V and VIII (Fig. 12-17), and the iron uptake protein Fet3 (Section A,l) are also closely related. 

Protein is formed mainly of polymerised amino-acids. The primary structure, unlike that of synthetic polymers, is non-repetitive and, for its production, requires a chemical template stored in the structure of the DNA molecule. The sizes of proteins vary considerably (in a range of molecular weights from 6000 to 1,000,000). Proteins fulfill many roles within the cell, the most important of which is that of catalysis. Proteins which have catalytic activity are called enzymes whilst other proteins have important roles in storage, transport, protection (antibodies), as chemical messengers (hormones) and in structure 17,, 8). 

In addition, a glycoprotein found in porcine uterine flushings contains iron and possesses acid phosphatase activity. This protein has been called uteroferrin, in view of its proposed role in the transport of iron from maternal to foetal circulation. On reduction, uteroferrin becomes pink in colour,... 

Chemical equilibria are important in numerous biological and environmental processes. For example, equilibria involving O2 molecules and the protein hemoglobin play a crucial role in the transport and delivery of oxygen from our lungs to our muscles. Similar equilibria involving CO molecules and hemoglobin account for the toxicity of carbon monoxide. 

SERCA pumps sequester Ca2+ in the ER lumen By maintaining appropriate Ca2+ concentrations in the ER lumen, SERCA pumps also play an essential role in protein synthesis, folding and transport of membrane and secreted proteins. This involves in particular chaperone-dependent processing and post-translational modifications which require a unique calcium rich environment. Chaperone molecules such as calreticulin and calnexin are involved in the quality control pathway in the ER (Berridge, 2002 Ellgaard and Helenius, 2003 Michalak et al., 2002). 

As was indicated earlier, the circulatory system and components in the blood stream are primarily responsible for the transport of toxicants to target tissues or reservoirs. Erythrocytes and lymph can play important roles in the transport of toxicants, but compared to plasma proteins, their role in toxicant distribution is relatively minor for most toxicants. Plasma protein binding can affect distribution because only the unbound... 

Facilated diffusion also involves the use of a carrier protein. It differs from active transport in that it occurs from a high to a low concentration and so does not require energy to be supplied by the cell. However, falicilated diffusion appears to play a minor role in the transport of drugs through membranes. 

Soulages J. L. and Wells M. A. (1994) Lipophorin the structure of an insect lipoprotein and its role in lipid transport in insects. Adv. Protein. Chem. 45, 371-415. 

Cartron ML, Mitchell SA, Woodhall MR et al (2007) Preliminary X-ray diffraction analysis of YcdB from Escherichia colt a novel haem-containing and Tat-secreted periplasmic protein with a potential role in iron transport. Acta Crystallogr Sect F Struct Biol Cryst Commun 63 37 11... 

When vitamin A stores are adequate, the liver secretes retinol bound to retinol-binding protein (RBP) into the circulation to provide tissues with a constant supply of vitamin A. In the circulation, the retinol-RBP complex is found bound to another circulating protein of hepatic origin, transthyretin (TTR). TTR also binds thyroid hormone and consequently plays a role in the transport of both vitamin A and thyroid hormone. The molecular size of the retinol-RBP complex is quite small, and the formation of the... 

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