mannoz6phosphate

Mannose-6-phosphate (M6P) is a phosphorylated form of mannose, a monosaccharide. In biological systems, M6P plays a crucial role in the intracellular targeting and sorting of specific proteins, particularly lysosomal enzymes. This modification occurs in the cis-Golgi network, where an enzyme called N-acetylglucosamine-1-phosphotransferase recognizes and binds to specific mannose residues on newly synthesized proteins destined for the lysosome. The enzyme then transfers a GlcNAc-phosphate group to the mannose residue. Subsequently, the GlcNAc is removed, leaving the mannose-6-phosphate tag. This M6P tag acts as a signal, directing these proteins to a mannose-6-phosphate receptor found on the lysosomal membrane. Upon binding to the receptor, the proteins are either delivered to the lysosome or secreted from the cell if the receptor is located on the cell surface. Deficiencies in the enzymes responsible for M6P tagging or in the M6P receptor can lead to lysosomal storage diseases, where essential lysosomal enzymes are not delivered to their proper destination, resulting in the accumulation of undigested materials within cells. M6P is therefore a critical molecular signal in protein trafficking and cellular function.