Aquaporins, function and discovery
Aquaporins are "the plumbing system for cells," said Agre. Every cell is primarily water. "But the water doesn’t just sit in the cell, it moves through it in a very organized way. The process occurs rapidly in tissues that have these aquaporins or water channels."
For many years, scientists assumed that water leaked through the cell membrane, and some water does. "But the very rapid movement of water through some cells was not explained by this theory," said Agre.
Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Also known as water channels, aquaporins are integral membrane pore proteins. Some of them, known as aquaglyceroporins, also transport other small uncharged solutes, such as glycerol, CO2, ammonia and urea across the membrane, depending on the size of the pore. For example, the aquaporin 3 channel has a pore width of 8-10 Ångströms and allows the passage of hydrophilic molecules ranging between 150-200 Da. However, the water pores are completely impermeable to charged species, such as protons, a property critical for the conservation of the membrane's electrochemical potential.
Water molecules traverse through the pore of the channel in single file. The presence of water channels increases membrane permeability to water.
Many human cell types express them, as do certain bacteria and many other organisms, such as plants for which it is essential for the water transport system.
Agre said he discovered aquaporins "by serendipity." His lab had an N.I.H. grant to study the Rh blood group antigens. They isolated the Rh molecule but a second molecule, 28 kilodaltons in size (and therefore called 28K) kept appearing. At first they thought it was a piece of the Rh molecule, or a contaminant, but it turned out to be an undiscovered molecule with unknown function. It was abundant in red blood cells and kidney tubes, and related to proteins of diverse origins, like the brains of fruit
For many years, scientists assumed that water leaked through the cell membrane, and some water does. "But the very rapid movement of water through some cells was not explained by this theory," said Agre.
Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Also known as water channels, aquaporins are integral membrane pore proteins. Some of them, known as aquaglyceroporins, also transport other small uncharged solutes, such as glycerol, CO2, ammonia and urea across the membrane, depending on the size of the pore. For example, the aquaporin 3 channel has a pore width of 8-10 Ångströms and allows the passage of hydrophilic molecules ranging between 150-200 Da. However, the water pores are completely impermeable to charged species, such as protons, a property critical for the conservation of the membrane's electrochemical potential.
Water molecules traverse through the pore of the channel in single file. The presence of water channels increases membrane permeability to water.
Many human cell types express them, as do certain bacteria and many other organisms, such as plants for which it is essential for the water transport system.
Agre said he discovered aquaporins "by serendipity." His lab had an N.I.H. grant to study the Rh blood group antigens. They isolated the Rh molecule but a second molecule, 28 kilodaltons in size (and therefore called 28K) kept appearing. At first they thought it was a piece of the Rh molecule, or a contaminant, but it turned out to be an undiscovered molecule with unknown function. It was abundant in red blood cells and kidney tubes, and related to proteins of diverse origins, like the brains of fruit