Image: Aquaporins

Caption1: Here we see water molecules passing single-file through a channel of the membrane protein aquaporin.
This simulation, which includes over 100,000 molecules, shows that water molecules do a mid-channel flip, which we can see here. These channels conduct water through cells at up to a billion molecules per second, yet block hydrogen ions from entering. When impaired, aquaporins play a role in cataracts and diabetes.

Caption2: Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. These channels are widely distributed in all kingdoms of life, including bacteria, plants, and mammals. More than ten different aquaporins have been found in human body, and several diseases, such as congenital cataracts and nephrogenic diabetes insipidus, are connected to the impaired function of these channels. They form tetramers in the cell membrane, and facilitate the transport of water and, in some cases, other small solutes across the membrane. They are, however, completely impermeable to charged species, such as protons, a remarkable property that is critical for the conservation of membrane's electrochemical potential, but paradoxical at the same time, since protons can usually be transported readily through water molecules. The results of our simulations have now provided new insight into the mechanism underlying this fascinating property. Water molecules passing the channel are forced, by the protein's electrostatic forces, to flip at the center of the channel (see the animation), thereby breaking the alternative donor-acceptor arrangement that is necessary for proton translocation

Source: F. Zhu, Univ. of Illinois at Urbana-Champaign


NSF Funded: yes

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