Explain how the aquaporin polypeptides are transported from the golgi complex and inserted into the plasma membrane.
Question: Explain how the aquaporin polypeptides are transported from the golgi complex and inserted into the plasma membrane.
Aquaporins are channel proteins that facilitate the transport of water and other small molecules across the plasma membrane. They have six membrane-spanning alpha helical domains with both carboxylic and amino terminals on the cytoplasmic side. Two hydrophobic loops contain conserved asparagine – proline – alanine (\"NPA motif\") which form a barrel surrounding a central pore-like region that contains additional protein density .
Aquaporins are sorted in the trans-Golgi network (TGN) via lipid rafts and delivered to the plasma membrane by vesicular transport . The specificity and regulation of aquaporin trafficking depend on the subfamily and isoform of the aquaporin, as well as the cell type and environmental conditions . For example, aquaporin-3 and aquaporin-4 are sorted differently and require different motifs for their apical or basolateral localization in kidney cells .
To explain how the aquaporin polypeptides are transported from the golgi complex and inserted into the plasma membrane, we can use the following steps:
1. The aquaporin polypeptides are synthesized in the endoplasmic reticulum (ER) and folded into their tertiary structure with the help of chaperone proteins.
2. The aquaporin polypeptides are transported from the ER to the golgi complex by coat protein complex II (COPII)-coated vesicles.
3. The aquaporin polypeptides are modified in the golgi complex by glycosylation and phosphorylation, which may affect their sorting and function.
4. The aquaporin polypeptides are sorted in the TGN by lipid rafts, which are microdomains of the membrane enriched in cholesterol and sphingolipids.
5. The aquaporin polypeptides are packaged into vesicles that bud from the TGN and are targeted to the plasma membrane by specific signals or receptors.
6. The aquaporin polypeptides are inserted into the plasma membrane by fusion of the vesicles with the membrane, mediated by SNARE proteins.
7. The aquaporin polypeptides are distributed in the plasma membrane according to their subcellular localization, which may be apical, basolateral or both.
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