title: Functional comparison of the two Bacillus anthracis glutamate racemases.
abstract: Glutamate racemase activity in Bacillus anthracis is of significant interest with respect to chemotherapeutic drug design, because L-glutamate stereoisomerization to D-glutamate is predicted to be closely associated with peptidoglycan and capsule biosynthesis, which are important for growth and virulence, respectively. In contrast to most bacteria, which harbor a single glutamate racemase gene, the genomic sequence of B. anthracis predicts two genes encoding glutamate racemases, racE1 and racE2. To evaluate whether racE1 and racE2 encode functional glutamate racemases, we cloned and expressed racE1 and racE2 in Escherichia coli. Size exclusion chromatography of the two purified recombinant proteins suggested differences in their quaternary structures, as RacE1 eluted primarily as a monomer, while RacE2 demonstrated characteristics of a higher-order species. Analysis of purified recombinant RacE1 and RacE2 revealed that the two proteins catalyze the reversible stereoisomerization of L-glutamate and D-glutamate with similar, but not identical, steady-state kinetic properties. Analysis of the pH dependence of L-glutamate stereoisomerization suggested that RacE1 and RacE2 both possess two titratable active site residues important for catalysis. Moreover, directed mutagenesis of predicted active site residues resulted in complete attenuation of the enzymatic activities of both RacE1 and RacE2. Homology modeling of RacE1 and RacE2 revealed potential differences within the active site pocket that might affect the design of inhibitory pharmacophores. These results suggest that racE1 and racE2 encode functional glutamate racemases with similar, but not identical, active site features.
authors.affiliation: Department of Microbiology, Institute for Genomic Biology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Dylan
authors.initials: D
authors.lastname: Dodd
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Reese
authors.forename: Craig R
authors.initials: CR
authors.lastname: Louer
authors.forename: Jimmy D
authors.initials: JD
authors.lastname: Ballard
authors.forename: M Ashley
authors.initials: MA
authors.lastname: Spies
authors.forename: Steven R
authors.initials: SR
authors.lastname: Blanke
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001408:Bacillus anthracis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002850:Chromatography, Gel; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013237:Stereoisomerism; D040681:Structural Homology, Protein
chemical_list: D001426:Bacterial Proteins; D007527:Isoenzymes; D011994:Recombinant Proteins; D018698:Glutamic Acid; D000591:Amino Acid Isomerases; C062292:glutamate racemase