|Protein name||S-methyl-5''-thioadenosine phosphorylase||S-methyl-5''-thioadenosine phosphorylase||S-methyl-5'-thioadenosine phosphorylase5'-methylthioadenosine nucleosidase5'-deoxy-5'-methylthioadenosine phosphorylaseMTA phosphorylaseMeSAdo phosphorylaseMeSAdo/Ado phosphorylasemethylthioadenosine phosphorylasemethylthioadenosine nucleoside phosphorylase5'-methylthioadenosine:phosphate methylthio-D-ribosyl-transferaseS-methyl-5-thioadenosine phosphorylaseS-methyl-5-thioadenosine:phosphateS-methyl-5-thio-alpha-D-ribosyl-transferase|
|Synonyms||EC 18.104.22.1685''-methylthioadenosine phosphorylaseMTA phosphorylaseMTAPase||EC 22.214.171.1245''-methylthioadenosine phosphorylaseMTA phosphorylase|
|Activity||S-methyl-5''-thioadenosine + phosphate = adenine + S-methyl-5-thio-alpha-D-ribose 1-phosphate.||S-methyl-5''-thioadenosine + phosphate = adenine + S-methyl-5-thio-alpha-D-ribose 1-phosphate.|
|References for Catalytic Mechanism|
|References||Sections||No. of steps in catalysis|
|Authors||Mao C, Cook WJ, Zhou M, Koszalka GW, Krenitsky TA, Ealick SE|
|Title||The crystal structure of Escherichia coli purine nucleoside phosphorylase: a comparison with the human enzyme reveals a conserved topology.|
|Journal||Eur J Biochem|
|Authors||Allart B, Gatel M, Guillerm D, Guillerm G|
|Title||The catalytic mechanism of adenosylhomocysteine/methylthioadenosine nucleosidase from Escherichia coli--chemical evidence for a transition state with a substantial oxocarbenium character.|
|Journal||Structure Fold Des|
|Authors||Appleby TC, Erion MD, Ealick SE|
|Title||The structure of human 5'-deoxy-5'-methylthioadenosine phosphorylase at 1.7 A resolution provides insights into substrate binding and catalysis.|
|Journal||J Biol Chem|
|Authors||Appleby TC, Mathews II, Porcelli M, Cacciapuoti G, Ealick SE|
|Title||Three-dimensional structure of a hyperthermophilic 5'-deoxy-5'-methylthioadenosine phosphorylase from Sulfolobus solfataricus.|
|Authors||Lee JE, Cornell KA, Riscoe MK, Howell PL|
|Title||Structure of E. coli 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase reveals similarity to the purine nucleoside phosphorylases.|
|This enzyme belongs to the PNP phosphorylase family.|
The catalysis of this enzyme is generally thought to proceed via a two-step mechanism with formation of an oxocarbenium-like transition state followed by a nucleophilic attack by the phosphate ion at the anomeric carbon in an SN1-like mechanism, according to the literature .
Negatively charged residues such as histidine and arginine are involved in phosphate-binding. One of the oxygen atoms of this phosphate ion is in a good position to initially stabilize the partial positive charge on O4' atom of the proposed oxocarbenium ion intermediate . The oxygen atom of the phosphate will make a nucleophilic attack at the anomeric carbon, C1'.
Moreover, a buried aspartic acid residue, Asp220 (PDB; 1cg6), can exhibit a significant increase in pKa, which allows it to be protonated under physiological conditions, according to the paper . If the case is, this aspartic acid residue can protonate N7 of the adenine base, in order to accommodate the flow of negative charge into the base that occurs during the bond cleavage .