Mannose 6-phosphate

Mannose 6-phosphate

Chemical structure of Mannose 6-phosphate

Mannose 6-phosphate (M6P) is a carbohydrate molecule that plays a crucial role in the lysosomal enzyme targeting pathway. It is a derivative of mannose, a type of hexose sugar, and is phosphorylated at the sixth carbon position. This molecule is essential for the proper functioning of the lysosome, an organelle responsible for the degradation of macromolecules.

Function

Mannose 6-phosphate serves as a key signal for the transport of lysosomal enzymes from the Golgi apparatus to the lysosome. These enzymes are tagged with M6P in the cis-Golgi network, which allows them to be recognized by mannose 6-phosphate receptors (MPRs) in the trans-Golgi network. The MPRs bind to the M6P-tagged enzymes and facilitate their packaging into transport vesicles that deliver them to the lysosome.

Biosynthesis

The synthesis of mannose 6-phosphate begins with the phosphorylation of mannose. This process is catalyzed by the enzyme phosphomannomutase, which converts mannose 1-phosphate to mannose 6-phosphate. The phosphorylation is crucial for the subsequent recognition and binding by MPRs.

Clinical Significance

Defects in the mannose 6-phosphate pathway can lead to severe lysosomal storage disorders. One such disorder is I-cell disease, also known as mucolipidosis II, where there is a deficiency in the enzyme responsible for adding the phosphate group to mannose. This results in the misdirection of lysosomal enzymes, leading to their secretion outside the cell instead of being delivered to the lysosome.

Related pages

• Lysosome
• Golgi apparatus
• Hexose
• I-cell disease