N-acetylglucosamine-1-phosphate transferase

N-acetylglucosamine-1-phosphate transferase (GlcNAc-1-phosphotrasferase) is a transferase enzyme.

Function
It is made up of two alpha (α), two betas (β), and two gammas (γ) subunits. GNPTAB produces the alpha and beta subunits, GNPTG produces the gamma subunit. GlcNAc-1-phosphotransferase functions to prepare newly made enzymes for lysosome transportation (lysosomal hydrolases to the lysosome). Lysosomes, a part of an animal cell, helps break down large molecules into smaller ones that can be reused. GlcNAc-1-phosphotransferase phosphorylates carbon 6 of one or more mannosyl residues of N linked glycoproteins being processed in Golgi Apparatus. UDP-GLcNAc provides the phosphate in a reaction catalysed by this enzyme. M6P acts as an indicator of whether a hydrolase should be transported to the lysosome or not. Once a hydrolase indicates an M6P, it can be transported to a lysosome. Surprisingly some lysosomal enzymes are only tagged at a rate of 5% or lower.

Clinical significance
It is associated with the following conditions:
 * mucolipidosis II alpha/beta (I-cell disease) - GNPTAB
 * mucolipidosis III alpha/beta (pseudo-Hurler polydystrophy) - GNPTAB
 * mucolipidosis III gamma - GNPTG
 * stuttering (Kang et al., 2010)

In melanocytic cells, GNPTG gene expression may be regulated by MITF.