Exploring the GnT I protein

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This website will elucidate the intricacies of the protein N-acetylglucosaminyltransferase I (GnT I).

To go back to the original image, click here.

There are several extremely interesting specifics of this protein. GnT I is a sugar transferase and it's job in the cell is to add sugars to the membranes of cells. These sugars are essential in cell-to-cell interactions, and mutations in proteins with a similar function or enzymes that are dependent on GnT I action is associated with human disease and metastasis.

First, let's look at the protein itself. GnT-1 has two domains, an N-terminal domain which shown here , and a C-terminal domain shown here . The two domains are connected by a linker region highlighted here in blue . This domain wraps halfway around domain 1 before starting the first helix of domain 2.

GnT I forms a complex with UDP-GlcNAc (an oligosaccharide to be added to the outside of the cell) and a Mn2+ ion in its active form. Click here to see the area where UDP-GlcNAc binds. Click here to add UDP-GlcNAc and here to add the Manganese ion.

This complex now allows GnT I to bring a nucleotide sugar and the oligosaccharide acceptor together. To view this easily, let's look at the secondary structure of GnT I and then more specifically in this region . Click here to see the pocket that is formed by GnT1: three alpha helices (in red) and one beta pleated sheet create a pocket for the nucleotide sugar and oligosaccharide receptor. This pocket is highly acidic, and the proposed catalytic base (Asp 291) is also highlighted in green.

Now let's add our UDP-GlcNAc and Mn2+ complex . GnT I is now ready to perform its function.

Reference:

Unligil UM, Zhou S, Yuwaraj S, Sarkar M, Schachter H, Rini JM. "X-ray crystal structure of rabbit N-acetylglucosaminyltransferase I: catalytic mechanism and a new protein superfamily." EMBO J. 2000 Oct 16;19(20):5269-80.

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