glutaminase and ribulose-5-phosphate

Pyridoxal 5'-phosphate (PLP, vitamin B6), a cofactor in many enzymatic reactions, has two distinct biosynthetic routes, which do not coexist in any organism. Two proteins, known as PdxS and PdxT, together form a PLP synthase in plants, fungi, archaea, and some eubacteria. PLP synthase is a heteromeric glutamine amidotransferase in which PdxT produces ammonia from glutamine and PdxS combines ammonia with five- and three-carbon phosphosugars to form PLP. In the 2.2-A crystal structure, PdxS is a cylindrical dodecamer of subunits having the classic (beta/alpha)8 barrel fold. PdxS subunits form two hexameric rings with the active sites positioned on the inside. The hexamer and dodecamer forms coexist in solution. A novel phosphate-binding site is suggested by bound sulfate. The sulfate and another bound molecule, methyl pentanediol, were used to model the substrate ribulose 5-phosphate, and to propose catalytic roles for residues in the active site. The distribution of conserved surfaces in the PdxS dodecamer was used to predict a docking site for the glutaminase partner, PdxT.

Topics: Ammonia; Bacillus subtilis; Base Sequence; Binding Sites; Catalysis; Cloning, Molecular; Crystallography, X-Ray; Escherichia coli; Glutaminase; Glutamine; Glycols; Models, Chemical; Models, Molecular; Models, Statistical; Molecular Sequence Data; Nitrogenous Group Transferases; Phosphorylation; Plasmids; Protein Binding; Protein Conformation; Protein Folding; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Pyridoxal Phosphate; Ribulosephosphates; Substrate Specificity