Amino acid transporters structure

Shafqat, S., Tamarappoo, B. K., Kilberg, M. S., Puranam, R. S., McNamara, J. O., Guadano-Ferraz, A., and Fremeau, R. T. (1993) Cloning and expression of a novel Na+-dependent neutral amino acid transporter structurally related to mammalian Na+/glutamate cotransporters. J. Biol. Chem. 268,15351-15355. 

Babu E, Kanai Y, Chairoungdua A, Kim do K, Iribe Y, Tangtrongsup S, Jutabha P, Li Y, Ahmed N, Sakamoto S, Anzai N, Nagamori S, Endou H. Identification of a novel system L amino acid transporter structurally distinct from heterodimeric amino acid transporters. J Biol Chem 2003 278 43838-43845. 

Despite the limited information available, rather clear predictions can be made about the probable structure, location, and energy coupling of the amino acid transporters of Saccharomyces cerevisiae, by comparing them with better known systems in both prokaryotes and eukaryotes. 

Substantial progress can be expected in the near future concerning the structure of amino acid transporters, their functional dissection, and their evolutionary filiation. 

Kim, D. K., et al. Expression cloning of a Na+-independent aromatic amino acid transporter with structural similarity to H+/monocarboxylate transporters. J. Biol. Chern. 2001, 276, 17221-17228. 

Arriza, J. L., Kavanaugh, M. P., Fairman, W. A., Wu, Y.-N., Murdoch, G. H., North, R. A., and Amara, S. G. (1993) Cloning and expression of a human neutral amino acid transporter with structural similarity to the glutamate transporter gene family. J. Biol. Chem. 268, 15329-15332. 

The inhibition of amino-acid transport has been regarded as the main toxic effect of mercury compounds [82], The biochemical mechanism underlying the inhibition is unclear. In unfertilized sea-urchin eggs an interaction with the amino-acid carrier was found, whereas in fertilized eggs inhibition of amino-acid transport was indirect and might result from an elevation of the Na + content of the egg caused by the inhibition of the Na+ pump [83]. The action on the diffusional process could be mediated by an effect on membrane phospholipids or on membrane proteins, or by interaction with Ca2+ which stabilizes membrane structure. Mercuric chloride in skate liver cells inhibited amino acid transport, decreased Na + /K + -ATPase (adenosinetriphosphatase) activity, impaired volume regulatory mechanisms and increased the permeability of the plasma membrane to potassium [84]. It has been suggested that... 

Amino acid transporters, oligopeptide transporters, glucose transporters, lactic acid transporters, monocarboxylic acid transporters, phosphate transporters, bile acid transporters and other transporters present on the apical membrane of the epithelial cells serve as carriers to facilitate nutrient absorption by the intestine. On the basolateral membrane, amino acid and oligopeptide transporters also exist. Drag moieties possessing similar structures to nutrients that are absorbed by such carriers may also be absorbed in this manner. 

Therefore, the three vitamin deficiencies so far studied in detail appear to affect amino acid transport and accumulation in similar but indirect ways. The accumulation defect is most pronounced in vitamin B6-deficient cells, for which there is also strong evidence implicating an abnormality in cell wall composition as a likely source of the change in transport activity. Direct evidence for a cell wall change in biotin- and pantothenate-deficient cells has not yet been obtained. The possibility remains, therefore, that the change in accumulation activity may be caused by an abnormality in some other structural component such as the peripheral cell membrane. 

To date, the most extensively studied natural ionophore is gramicidin,10 a polypeptide antibiotic isolated from the bacterium Bacillus brevis. Indeed, the idea of a channel-like structure for ion transport was inferred from its study. However, unlike channel proteins, which are exclusively composed of L-amino acids, each alternate amino acid in gramicidin has D-stereochemistry. It is composed of 16 residues, 15 of which are amino acids. The structure is summarized below, in which Xxx has the following identities gramicidin A (gA), Trp gB, Phe gC, Tyr gD, a mixture of gA, gB, gC, -80 5 15. 

R. L. Preston,). E Schaeffer, and P E Curran, Structure-affinity relationships of substrates for the neutral amino acid transport system in rabbit ileum, /. Gen. Physid., 64 443-467 (1974). 

K. A., Miyauchi, S., Huang, W., Thwaites, D.T. and Ganapathy, V. (2003) Structure, function and immunolocalization of a proton-coupled amino acid transporter (hPATl) in the human intestinal cell line Caco-2. The Journal of Physiology, 546 (Pt 2), 349-361. 

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