Write a 100-350 word essay about the enzyme human PMM2. Provide information related to enzyme: i) function, ii) reaction pathways, ii) Location, and iv) diseases. In writing include these four subheadings

### Function
Human PMM2, or phosphomannomutase 2, is a crucial enzyme in the glycosylation process, responsible for the interconversion of mannose-6-phosphate and mannose-1-phosphate. This conversion is essential for the synthesis of GDP-mannose, a sugar nucleotide required for the glycosylation of proteins and lipids. Glycosylation is a key process that modifies proteins and lipids, influencing their structure, function, and stability, which is vital for proper cellular function.

### Reaction Pathways
PMM2 operates in the mannose metabolism pathway, where it catalyzes the reversible conversion of mannose-6-phosphate to mannose-1-phosphate. The product, mannose-1-phosphate, is then converted to GDP-mannose, a critical donor molecule in the glycosylation of proteins and lipids. This process is essential for the synthesis of glycoproteins and glycolipids, which are involved in cell signaling, immune responses, and the formation of cell membranes. PMM2’s function is integral to ensuring that cells can properly glycosylate proteins and lipids, which is essential for many physiological processes.

### Location
PMM2 is primarily localized in the cytoplasm, where it carries out its role in carbohydrate metabolism and glycosylation. The cytoplasmic environment allows PMM2 to efficiently convert mannose-6-phosphate to mannose-1-phosphate, ensuring a steady supply of GDP-mannose for glycosylation. This localization is critical for maintaining the proper function of cellular glycosylation pathways.

### Diseases
Mutations in the PMM2 gene are the most common cause of congenital disorders of glycosylation (CDG), specifically CDG type Ia (PMM2-CDG). This rare genetic disorder is characterized by a wide range of symptoms, including developmental delays, neurological issues, liver dysfunction, and coagulation problems. The disease arises from impaired PMM2 activity, leading to deficient glycosylation of proteins and lipids, which disrupts various cellular functions. PMM2-CDG highlights the critical role of PMM2 in human health, and ongoing research aims to develop therapies to manage or correct the glycosylation defects caused by PMM2 mutations.