A new study from Cornell University sheds light on how cells help wipe out 'biological waste' from the body, which if accumulates can lead to many diseases, including Alzheimer's, cystic fibrosis and developmental disorders.
The researchers revealed that cells have developed complex systems for recycling, reusing and disposing of damaged, non-functional waste proteins.
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Cells use enzymes known as proteases to break down proteins into their component amino acids in the cytoplasm the fluid inside the cell's surface membrane. Those amino acids are then reused to make new proteins.
But water-insoluble proteins embedded in the cell's membrane require a much more complicated recycling process.
The research team led by Scott Emr, director of the Weill Institute for Cell and Molecular Biology at Cornell identified a family of proteins that controls the removal of unwanted water-insoluble proteins from the membrane.
During the study, the researchers identified nine related proteins in yeast, which they named the "arrestin-related trafficking" adaptors or ARTs. They are also found in humans.
Each of these proteins identifies and binds to a different set of membrane proteins. Once bound, they link to an enzyme that attaches a chemical tag for that protein's removal.
Once the protein is tagged, the piece of membrane with the targeted protein forms a packet, called a vesicle that enters the cell's cytoplasm.
There, the vesicle enters a larger membrane body called an endosome, which in turn dumps it into another compartment called the lysosome, where special enzymes break apart big molecules to their core units: proteins to amino acids, membranes to fatty acids, carbohydrates to sugars and nucleic acids to nucleotides, and those basic materials are then reused.
The findings are published in the journals Cell and Developmental Cell.