The way we look at some things is easily understandable. By the way, we are already familiar with the term, Aquaporins which we get in their name “aqua means water, porins indicates the pores in the membrane. So we can come to know that it conducts water”. But there are many functions that we need to know about the Aquaporins because our body contains about 60% water, which signifies that aquaporins play an essential role in transportation. Primary Reason for conducting water: OSMOREGULATION
How is it capable of allowing only water to pass through the cell membrane?
Most channels have the transmembrane from the hydrophobic (water-hating) region. But here in aquaporins, an integral protein forms a hydrophilic part in the transmembrane, which provides the rapid movement of water molecules. Two examples to quickly understand their functions:
1. In humans, Erythrocytes, when passing renal medulla as blood, have 2×105 copies of AQP-1 per cell. ⇨ In nephrons (functional units of the kidney), the membranes of proximal renal tube cells have five different aquaporins types. ⇨ These cells reabsorb water from urine.
2. In plants, aquaporins provide the rapid movement of water across the membrane to make turgor pressure possible. Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. Without this, there will be the loss of water, lacks mechanical support and results in wilt (Bend and start to die due to lack of water).
Is it possible for any proton like H3O+ to pass through this?
Let’s see how it takes water explicitly alone. First of all, Aquaporins have structure specificity. It has four monomers (forms a tetramer). So by this, aquaporin has four pores, each at four monomers having a size that only water can pass through. Three essential amino acids in aquaporin (AQP): Asparagine-Proline-Alanine (NPA). NPA loops in short helices form-critical arginine and histidine, and this provides a positive charge in positions that repel any protons like Hydronium ions.
There are about 10 AQP in humans. Their functions depend on their locations.
In transportation, many channels and pumps(such as Na-K pumps) are operated by the cells; this (AQP) is important as other transporting membrane proteins and have a unique way of allowing specific molecules.
Disease-related to aquaporins:
1. Diseases associated with the aquaporins are called aquaporinopathies. In humans, the most common condition is nephrogenic diabetes insipidus (NDI), a non-X-linked disease caused by the mutations in AQP-2.
2. The mutations in AQP-0 cause congenital cataracts.
3. The autoimmune reactions against AQP-4 in humans causes Devic’s disease.