Sandbox Reserved 982

Structural Highlights

Stx is composed of two main subunits labeled A and B. The A subunit bonds noncovalently to the B subunit. The A subunit is 293 amino acids long with its active site being glutamic acid 167. Studies have shown that the first 239 residues are essential for the enzymatic activity of the A subunit. The B subunit is a pentamer that resembles a star and can be divided into five identical subunits. Each of the subunits is 69 amino acids in length. The purpose of the B subunit is to bind to globotriaosylceramide (GB3) which is a glycosphingolipid that resides on the surface of some Eukaryotic cells. Each monomer of the B subunit has three binding sites for GB3 making the protein very potent (Melton-Celsa 2013).

Function

The pathway of stx entering a cell begins with the B subunit’s binding to GB3. Once this occurs, the A subunit disconnects from the B subunit and enters the cell through endocytosis. Using retrograde transport the A subunit passes through the Golgi apparatus and the rough endoplasmic reticulum. In the rough endoplasmic reticulum, the A subunit is cleaved into two parts called A1 and A2. A2 is degraded, but A1 freely enters the cytosol (Sandvig 2000). Once in the cytosol, A1 acts as an N-glycosidase, which is an enzyme that hydrolyzes bonds that link sugars. With this enzymatic activity, A1 removes adenines from the 28S RNA of the 60S ribosomal subunit (Melton-Celsa 2013). This inhibits protein synthesis and ultimately leads to cell death.

Disease and It's Pathogenesis

This is a sample scene created with SAT to by Group, and another to make of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes.