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Bacterial Leucine Transporter (LeuT) is a bundled twelve alpha helix protein which belongs to the family of transporters that shuttle amino acids in and out of bacterial cells. Specialized in small hydrophobic amino acids such as leucine and alanine, this transporter is powered by the gradient of sodium ions that is normally maintained by healthy cells across their membranes. LeuT acts as a symporter, which means that it links the passage of a sodium ion across the cell membrane with the transport of the amino acid in the same direction. It was first crystallized to understand the inner molecular mechanisms of antidepressant's work since it has a close resemblance with the human neurotransmitter transporters (more difficult to crystallize) that these drugs block, thus inhibiting the reuptake of chemical messengers across the cell membrane of nerve axons and glial cells.〔〔 ==Structure== LeuT is an homodimer composed by two identical subunits which are in contact in two points. Each of these polypeptide chains is about 70 Å tall and has a diameter of 48 Å. Its formula weight is 58078.2 kDa.〔A competitive inhibitor traps LeuT in an open-to-out conformation. ("Protein Data Base" )〕 It is mainly made of hydrophobic residues. These are in contact with the inside of the bilayer, while the hydrophilic residues are in contact with the extracellular and intracellular space. Taking into account that it is a transmembrane protein, this is a relevant characteristic, as it can interact both with water and phospholipids. This transporter’s secondary structure consists of twelve alpha helices and two short beta strands. Some loops can also be found linking them. As LeuT is a symporter and uses the electrochemical potential of sodium ions to facilitate leucine’s transport, both sodium ions and the hydrophobic amino acid, Leucine (Leu), bind to the centre of this protein. The residues involved in this binding are situated on the transmembrane alpha helix segments 1, 3, 6 and 8.〔Singh SK, Piscitelli CL, Yamashita A, Gouaux E (2008) A competitive inhibitor traps LeuT in an open-to-out conformation. Science 322, 1655-61 ("A competitive inhibitor traps LeuT in an open-to-out conformation" )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bacterial Leucine Transporter」の詳細全文を読む スポンサード リンク
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