2gcb
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G51S/S52T double mutant of L. casei FPGS
OverviewOverview
Based upon the three-dimensional structure of Lactobacillus casei, folylpolyglutamate synthetase (FPGS), site-directed mutagenesis studies, were performed on three residues associated with the ATPase site: Gly51, Ser52 and Ser73. Gly51 and Ser52 are at the end of the P-loop, which is, involved in triphosphate binding. A G51S mutant enzyme and a G51S/S52T, double-mutant enzyme were made in order to alter the FPGS P-loop to more, closely resemble the sequences found in other ATPase and GTPase enzymes., Ser73 is on a neighboring loop (the Omega-loop) and precedes a proline, residue found to be in a cis conformation. The carbonyl O atom of Ser73 is, one of the protein ligands for the essential Mg(2+) ion involved in ATP, binding and hydrolysis and the Omega-loop is involved in binding the, folate substrate 5,10-methylenetetrahydrofolate. The serine residue was, mutated to alanine and this is the only one of the three mutants which, retains some FPGS activity. The structures of the G51S, G51S/S52T and S73A, mutant proteins have been solved to high resolution, along with the, structure of the apo wild-type FPGS. The P-loop in both the G51S and, G51S/S52T mutant proteins remains unaltered, yet both structures show a, large conformational rearrangement of the Omega-loop in which a cis-Pro, residue has switched conformation to a trans-peptide. The structure of the, Omega-loop is severely disrupted and as a consequence structural, rearrangements are observed in the peptide linker joining the two domains, of the enzyme. Magnesium binding in the active site is also disrupted by, the presence of the serine side chain at position 51 and by the, repositioning of the carbonyl O atom of Ser73 and a water molecule is, bound in place of the Mg(2+) ion. The S73A mutant protein retains the, cis-Pro configuration in the Omega-loop and the Mg(2+) site remains, intact. The cis-Pro is also observed in the structure of the, substrate-free form of FPGS (apoFPGS), maintained in the absence of Mg(2+), by a hydrogen-bonding network involving water molecules in the active, site. It is only in the complete absence of water or Mg(2+) in the binding, site that the cis-Pro switches to the trans conformation.
About this StructureAbout this Structure
2GCB is a Single protein structure of sequence from Lactobacillus casei. Active as Tetrahydrofolate synthase, with EC number 6.3.2.17 Full crystallographic information is available from OCA.
ReferenceReference
Mutation of Gly51 to serine in the P-loop of Lactobacillus casei folylpolyglutamate synthetase abolishes activity by altering the conformation of two adjacent loops., Smith CA, Cross JA, Bognar AL, Sun X, Acta Crystallogr D Biol Crystallogr. 2006 May;62(Pt 5):548-58. Epub 2006, Apr 19. PMID:16627949
Page seeded by OCA on Wed Nov 21 11:07:01 2007