SsMTAP

Steve Ealick's Research Group

5'-Deoxy-5'-methylthioadenosine Phosphorylase from Sulfolobus solfataricus (SsMTAP)

PDB files:

1JDU (native; space group C222₁)
1JE1 (with guanosine and sulfate; space group P2₁)
1JDS (with phosphate; space group P2₁)
1JDZ (with Formycin B and sulfate ion; space group C222₁)
1JDT (complexed with MTA and sulfate ion; space group C222₁)
1JDV (complexed with adenosine and sulfate ion; space group P2₁)
1JE0 (complexed with phosphate and tris; space group C222₁)
1JPV (complexed with sulfate; space group C222₁)
1JP7 (complexed with sulfate; space group C222₁)

Description:

5′-deoxy-5′-methylthioadenosine phosphorylasefrom Sulfolobus solfataricus (SsMTAP) functions in the purine salvage pathway where it catalyzes the phosphorolysis of 5′-deoxy-5′-methylthioadenosine (MTA). MTA is a sulfur-containing nucleoside that is generated as a byproduct of polyamine biosynthesis. The reaction products are adenine and 5-methylthio-D-ribose 1-phosphate. SsMTAP is a hyperthermophilic enzyme since its optimum temperature is greater than 120°C. We later determined the structure of a second SsMTAP (SsMTAPII).

The monomers of SsMTAP are identical subunits of approximately 27 kDa each. The central portion of the molecule is made up of a large eight-stranded mixed β- sheet.

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The molecule displays D₃ symmetry and can be described as a trimer of dimers with three symmetric intersubunit disulfide bonds linking the dimers to one another. The hexameric shape is very similar to that of E. coli purine nucleoside phosphorylase.

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Each SsMTAP monomer contains one active site, which is located near a dimer interface. The two active sites in the dimeric unit are related by a molecular twofold axis and are separated by about 20 Å. In this schematic diagram, the binding geometries of a) guanosine, b) adenosine, and c) MTA are shown.

Reference:

Appleby TC, Mathews II, Porcelli M, Cacciapuoti G, Ealick SE. Three-dimensional structure of a hyperthermophilic 5′-deoxy-5′-methylthioadenosine phosphorylase from Sulfolobus solfataricus. J. Biol. Chem. 276:39232-39242 (2001).