Mannose6phosphatemerkintä

Mannose-6-phosphate (M6P) is a critical post-translational modification of proteins, playing a vital role in their intracellular trafficking and sorting. This modification occurs primarily within the cis-Golgi apparatus of eukaryotic cells. A specific enzyme, N-acetylglucosamine-1-phosphotransferase, recognizes and binds to a particular sequence of amino acids on nascent lysosomal enzymes. It then transfers a mannose-1-phosphate group to the C6 hydroxyl group of mannose residues on these enzymes. Subsequently, a second enzyme cleaves off the N-acetylglucosamine, leaving a mannose-6-phosphate tag attached to the protein. This M6P tag acts as a molecular address, directing the protein to the lysosome. Receptors for M6P, located on the trans-Golgi network and the plasma membrane, bind to these tagged proteins and facilitate their transport to endosomes, which mature into lysosomes. Deficiencies in the enzymes responsible for M6P tagging or in the M6P receptors can lead to the accumulation of undigested substrates within cells, resulting in various lysosomal storage diseases. The M6P pathway is therefore essential for maintaining cellular homeostasis and preventing the buildup of toxic waste products.