# Transport and transport molecules

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## Aquaporin AQP-1

The structure of the AQP-1 was mainly deciphered by electron microscopic methods. The scientists from the Max Planck Institute for Biophysical Chemistry succeeded in tracking the movement of individual water molecules through an aquaporin channel in detail and in real time with the help of atomically resolved computer simulations. The following questions could be answered:

### Structure of the aquaporin AQP-1

The aquaporin proteins are embedded in the membrane and thus form the actual water pores. Most aquaporins have multiple transmembrane passages, e.g. AQP-1 four and AQP-2 six.

The walls of the pore are formed by six transmembrane helices (H1-H6), the N- and C-termini are intracellular. Two highly conserved sequence motifs asparagine-proline-alanine (NPA) in the loops HB and HE form the water channel of the pore.

How can the extremely high water transport rates ($3⋅109$ Water molecules / second) with the aquaporin structure?

A certain arrangement of hydrophobic and ionizable amino acids requires a suitable alignment of the water molecules. The ionizable amino acids can then form hydrogen bridges to the water molecules one after the other and thus control their movement and, at the same time, an exact orientation in the channel. This precise control of the passage of the water molecules results in high flow rates.

How does the selective exclusion of protons during water transport through the pore work?

Protons are transferred by the solvent water via the hydrogen bridges, which are continuously formed between the water molecules and then dissolved again. In order to break the hydrogen bonds around a water molecule, a supply of dehydration energy is necessary. In order for this endothermic process to be possible, alternative binding partners must be offered to the water molecule.

## Literature

 de Groot, B. L .; Grubmüller, H. (2001):Water Permeation Across Biological Membranes. In: Science. 294, 2353-2357 Heymann, J. B .; Engel, A. (1999):Aquaporins; Phylogeny, Structure, and Physiology of Water Channels. In: News Physiol. Sci.. 14, 187-193 Murata, K .; Mitsuoka, K .; Hirai, T .; Walz, T .; Agre, P .; Heymann, J. B .; Engel, A .; Fujiyoshi, Y. (2000):Structural determinants of water permeation through aquaporin-1. In: Nature. 407, 599-605

## Video: Membrane Transport: Animation. (July 2022).

In it something is. I thank for the information. I did not know it.

2. Barnet

Theater props come out

3. Aengus

You should tell it - a gross mistake.