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)


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.


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).

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