Uniporter

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Types of transport proteins

A uniporter is a protein that mediates membrane transport from a molecule. Other types of protein involved in membrane transport are antiporters and symporters .

properties

A uniporter is a membrane protein that enables the transport of a molecule ( uniport ) mostly through passive transport. The passive transport is energetically driven by diffusion along a gradient of the concentration of the transported type of molecule, which was occasionally built up elsewhere with the consumption of adenosine triphosphate . On the other hand, some Uniporters use ATP ( primarily active ) with the Antiport . Uniporters enable a form of facilitated diffusion .

Transport model

two-state four-step model: The diagram on the top left represents the Jardetzky model, the rest of the diagrams are King-Altman diagrams under different transport states.
S : substrate,
k n (underlined): rate-determining step (for GLUT-1 ),
➔: preferred route (s),
⤏: non-preferred route (s)

In the 1960s, Oleg Jardetzky proposed a general model ( alternating-access model or Jardetzky model) for vans, including the Uniporter, and it was the first attempt to hypothesize the relationship between thermodynamics and structure of a van. From a theoretical point of view, the Jardetzky model is a typical example of the so-called two - state system in physics, which has been widely used in biology. Especially in the case of MFS transporters, the model is known as the rocker switch model (German: tilting movement). The Jardetzky model assumes three characteristic features:

  • A transporter must have a cavity inside that is large enough to accommodate the substrate.
  • It must be able to adopt two different conformations in order for the molecular cavity to be open in one conformation on one side of the membrane and in the other on the opposite side.
  • It must contain a binding site for substrates in the cavity, the substrate affinity of which can be different in the two conformations.

The conformation of Uniporters is either intracellular (C in ) or extracellular (C out ). Each conformation can either be occupied by a substrate or unoccupied. Four steps are therefore necessary to describe a transport cycle. It should be noted in which state the transport system is: in equilibrium, under outflow or under inflow. For each of these states you can create your own King-Altman plot (King-Altman diagram). This results in the two-state four-step model for describing a Uniporter transport cycle.

One of the most intensively studied eukaryotic uniporters is the glucose transporter GLUT-1.

Individual evidence

  1. ^ MG Wolfersberger: Uniporters, symporters and antiporters. In: The Journal of experimental biology. Volume 196, November 1994, pp. 5-6, ISSN  0022-0949 . PMID 7823043 .
  2. ↑ Oleg Jardetzky: Simple Allosteric Model for Membrane Pumps. In: Nature. 211, 1966, p. 969, doi : 10.1038 / 211969a0 .
  3. ↑ R. Phillips, J. Kondev, J. Theriot: Physical biology of the cell . 2nd Edition. Garland Science, New York 2013, ISBN 978-0-8153-4450-6 .
  4. ↑ a b Xuejun C. Zhang, Lei Han: Uniporter substrate binding and transport: reformulating mechanistic questions. In: Biophysics Reports. 2, 2016, p. 45, doi : 10.1007 / s41048-016-0030-7 .
  5. ↑ J. Abramson, I. Smirnova, V. Kasho, G. Verner, HR Kaback, S. Iwata: Structure and mechanism of the lactose permease of Escherichia coli. In: Science . Volume 301, number 5633, August 2003, pp. 610-615, doi : 10.1126 / science.1088196 , PMID 12893935 .
  6. ↑ Y. Huang, MJ Lemieux, J. Song, M. Auer, DN Wang: Structure and mechanism of the glycerol-3-phosphate transporter from Escherichia coli. In: Science . Volume 301, number 5633, August 2003, pp. 616-620, doi : 10.1126 / science.1087619 , PMID 12893936 .
  7. ↑ S. Dang, L. Sun, Y. Huang, F. Lu, Y. Liu, H. Gong, J. Wang, N. Yan: Structure of a fucose transporter in at outward-open conformation. In: Nature . Volume 467, number 7316, October 2010, pp. 734-738, doi : 10.1038 / nature09406 , PMID 20877283 .
  8. ↑ A. Carruthers, J. DeZutter, A. Ganguly, SU Devaskar: Will the original glucose transporter isoform please stand up! In: American Journal of Physiology- Endocrinology and Metabolism. Volume 297, number 4, October 2009, pp. E836-E848, doi : 10.1152 / ajpendo.00496.2009 , PMID 19690067 , PMC 2763785 (free full text) (review).
  9. ↑ D. Deng, N. Yan: GLUT, SGLT, and SWEET: Structural and mechanistic investigations of the glucose transporters. In: Protein science: a publication of the Protein Society. Volume 25, Number 3, March 2016, pp 546-558, doi : 10.1002 / pro.2858 , PMID 26650681 , PMC 4815417 (free full text) (Review).

literature