Once in the ER, the polypeptides undergo co-translational glycosylation on selected asparagine residues. To unite the alpha and beta polypeptide chains, intrapolypeptide disulfide bonds form; these events result in the formation of a catalytically active enzyme. In order to target the lysosome, where the enzyme operates, phosphomannosyl recognition markers need to be generated. They are formed by the sequential action of a phosphotransferase that add UDP-N-acetylglucosamine to selected mannose residues and a phoshpdiesterase a-N-acetylglucosaminidase, that removes N-acetylglucosamine. These reactions occur in the ER and cis-Golgi; in the trans-Golgi, hexosaminidase containing the recognition markers combines with a mannose-6-phosphate receptor to form a complex that will be translocated to the lysome. In the lysosome, …show more content…
While Hex A and Hex B are able to hydrolyze many of the same substrates, only Hex A has the capacity ot utilize negatively charged substrates, including the primary substrates GM2 ganglioside. Gangliosides are considered glycolipids, characteristically located in vertebrate nervous tissues, consisting of a complex of sphingosine, fatty acid, hexose, and sialic acid (Figure 1). The shorthand nomenclature of GM2 refers to a ganglioside “G”, monosialic “M”, and “2” donotes it as the second monosialic ganglioside discovered. A GM2 ganglioside also rquires the presence of water soluble, lipid binding protein cofactor known as the GM2 activator. It forms a 1:1 complex with GM2 ganglioside that renders the whole complex water soluble. It acts both as a transport protein to deliver the ganglioside substrate to the lysome and, as well, interacts with Hex A to allow cleavage of the glycosidic bond by the alpha