Transporter cloning

Khew-Goodall Y., Grillo M., Getchell M., Danho W., et al. (1991). Vomeromodulin, a putative pheromone transporter cloning, characterization, and cellular-localization of a novel glycoprotein of lateral nasal gland. FASEB J 5, 2976-2982. 

Yan, N., et al. Distribution of mRNA of a Na(+)-independent neutral amino acid transporter cloned from rat kidney and its expression in mammalian tissues and Xenopus laevis oocytes. Proc. Natl. Acad. Sci. U. S. A. 1992, 89, 9982-9985. 

Wu, X., et al. Structural and functional characteristics and tissue distribution pattern of rat OCTN1, an organic cation transporter, cloned from placenta. Biochim. Biophys. Acta 2000, 1466, 315-327. 

Nguyen, T. T., et al. Human intestinal folate transport cloning, expression, and distribution of complementary RNA. Gastroenterology 1997, 3 32, 783-791. 

Wang, H., et al. Human placental Na+-dependent multivitamin transporter. Cloning, functional expression, gene structure, and chromosomal localization. J. Biol. Chem. 1999, 274, 14875-14883. 

Burckhardt BC, Wolff NA, Burckhardt G. Electrophysiologic characterization of an organic anion transporter cloned from winter flounder kidney (fROAT). J Am Soc Nephrol 2000 11 (1) 9-17. 

Thiamine absorption occurs primarily in the proximal small intestine by both a saturable (thiamine transporter) process at low concentration (Ipmol/L, or lower) and by simple passive diffusion beyond that, though percentage absorption diminishes with increased dose. The absorbed thiamine undergoes intracellular phosphorylation, mainly to the pyrophosphate, but at the serosal side 90% of the transferred thiamine is in the firee form. Thiamine uptake is enhanced by thiamine deficiency and reduced by thyroid hormone, diabetes, and ethanol ingestion. The gene for the specific thiamine transporter has been identified, and the transporter cloned. Thiamine is carried by the portal blood to the liver. The firee vitamin occurs in the plasma, but the coenzyme, TPP, is the primary cellular component. Approximately 30 mg is stored in the body with 80% as the pyrophosphate, 10% as triphosphate, and the rest as thiamine and its monophosphate. About half of the body stores are found in skeletal muscles, with much of the remainder in heart, liver, kidneys, and nervous tissues (including the brain, which contains most of the triphosphate). 

Eliasof S, Arriza JL, Leighton BH, Amara SG, Kavanaugh MP (1998b) Localization and function of five glutamate transporters cloned from the salamander retina. Vis Res 35 1443-1454. 

Dal G, Carrasco L, Carrasco N Cloning and characterization of the thyroid iodide transporter. Nature 1996 379 458. 

It should be noted that there are a variety of ion channels (Chapter 41) in most cells, for Na, K, Ca, etc. Many of them have been cloned in recent years and their dispositions in their respective membranes worked out (number of times each one crosses its membrane, location of the actual ion transport site in the protein, etc). They can be classified as indicated in Table 49-4. Cardiac muscle is rich in ion channels, and they are also... 

Pacholczyk, T, Blakely, RD and Amara, SG (1991) Expression cloning of a cocaine- and antidepressant-sensitive human noradrenaline transporter. Nature 350 350-353. 

As with other monoamines, the actions of 5-HT are terminated by its reuptake from the synapse by another member of the family of Na+/CU-dependent transporters. The 5-HT transporter has many features in common with its catecholamine equivalent (described fully in Chapter 8 see Fig. 8.7), including its presumed 12 transmembrane-spanning domains. However, the cloned 5-HT transporter has a for 5-HT of about 450 nM whereas its K for both noradrenaline and dopamine is some ten thousand-fold greater (Povlock and Amara 1997) which means that it is relatively selective for uptake... 

Figure 11.4 Blockers of GABA transport.The upper panel shows the structure of several GABA analogues that inhibit GABA transport into neurons or glia (see text). The lower panels show more recently developed compounds that exhibit selectivity for various cloned GABA transporters...

Recently, a potential cytosolic component of the MEP precursor pathway, xylulose kinase, has been cloned and tested for function in an Escherichia coli complementation system. " The kinase activates exogenous xylulose in the cytoplasm. DXP is the precursor for DXS, which resides in the plastid, suggesting the activated substrate must be transported into the plastid. Another xylulose kinase homologue in Arabidopsis that contains a plastid targeting sequence was not active in the E. coli system, suggesting that it may have some other function in the plastid. Perhaps plant and bacterial tissue cultures may be fed xylulose to condition accumulation of isoprenoid metabolites. 

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