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

### Function
Human NANS, or N-acetylneuraminic acid synthase, is an enzyme that plays a critical role in the biosynthesis of sialic acids, which are essential components of glycoproteins and glycolipids. NANS catalyzes the conversion of N-acetylmannosamine (ManNAc) and phosphoenolpyruvate (PEP) into N-acetylneuraminic acid (Neu5Ac), the most common form of sialic acid in humans. Sialic acids are involved in various cellular functions, including cell-cell communication, immune response, and pathogen recognition.

### Reaction Pathways
NANS functions within the sialic acid biosynthesis pathway, where it catalyzes a key step in the formation of Neu5Ac. After the initial production of ManNAc from UDP-N-acetylglucosamine (UDP-GlcNAc), NANS combines ManNAc with PEP to produce Neu5Ac. This sialic acid is then activated and attached to glycoproteins and glycolipids, influencing their stability, signaling capabilities, and interactions with other molecules. Sialylation, the addition of sialic acid to proteins and lipids, is crucial for the proper functioning of the nervous and immune systems, as well as for cellular communication.

### Location
NANS is localized in the cytoplasm, where it participates in the sialic acid biosynthesis pathway. The cytoplasmic localization allows NANS to access its substrates, ManNAc and PEP, and efficiently produce Neu5Ac, which is then used in the Golgi apparatus for the sialylation of glycoproteins and glycolipids. The enzyme’s cytoplasmic location is essential for integrating the sialic acid biosynthesis with other metabolic processes within the cell.

### Diseases
Mutations in the NANS gene are associated with a rare genetic disorder known as spondyloepimetaphyseal dysplasia, Genevieve type (SEMD-G). This condition is characterized by severe skeletal abnormalities, developmental delays, and intellectual disabilities. The disease results from a deficiency in Neu5Ac production, leading to impaired sialylation of glycoproteins and glycolipids, which affects various biological processes, including bone development and brain function. Understanding NANS’s role in sialic acid biosynthesis is crucial for diagnosing and developing potential therapies for SEMD-G and other disorders related to sialic acid metabolism.