Linked Life Data

17649980

Source:http://linkedlifedata.com/resource/pubmed/id/17649980

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
33
pubmed:dateCreated
2007-8-16
pubmed:databankReference
pubmed:abstractText
We assigned l-talarate dehydratase (TalrD) and galactarate dehydratase (GalrD) functions to a group of orthologous proteins in the mechanistically diverse enolase superfamily, focusing our characterization on the protein encoded by the Salmonella typhimurium LT2 genome (GI:16766982; STM3697). Like the homologous mandelate racemase, l-fuconate dehydratase, and d-tartrate dehydratase, the active site of TalrD/GalrD contains a general acid/base Lys 197 at the end of the second beta-strand in the (beta/alpha)7beta-barrel domain, Asp 226, Glu 252, and Glu 278 as ligands for the essential Mg2+ at the ends of the third, fourth, and fifth beta-strands, a general acid/base His 328-Asp 301 dyad at the ends of the seventh and sixth beta-strands, and an electrophilic Glu 348 at the end of the eighth beta-strand. We discovered the function of STM3697 by screening a library of acid sugars; it catalyzes the efficient dehydration of both l-talarate (kcat = 2.1 s-1, kcat/Km = 9.1 x 10(3) M-1 s-1) and galactarate (kcat = 3.5 s-1, kcat/Km = 1.1 x 10(4) M-1 s-1). Because l-talarate is a previously unknown metabolite, we demonstrated that S. typhimurium LT2 can utilize l-talarate as carbon source. Insertional disruption of the gene encoding STM3697 abolishes this phenotype; this disruption also diminishes, but does not eliminate, the ability of the organism to utilize galactarate as carbon source. The dehydration of l-talarate is accompanied by competing epimerization to galactarate; little epimerization to l-talarate is observed in the dehydration of galactarate. On the basis of (1) structures of the wild type enzyme complexed with l-lyxarohydroxamate, an analogue of the enolate intermediate, and of the K197A mutant complexed with l-glucarate, a substrate for exchange of the alpha-proton, and (2) incorporation of solvent deuterium into galactarate in competition with dehydration, we conclude that Lys 197 functions as the galactarate-specific base and His 328 functions as the l-talarate-specific base. The epimerization of l-talarate to galactarate that competes with dehydration can be rationalized by partitioning of the enolate intermediate between dehydration (departure of the 3-OH group catalyzed by the conjugate acid of His 328) and epimerization (protonation on C2 by the conjugate acid of Lys 197). The promiscuous catalytic activities discovered for STM3697 highlight the evolutionary potential of a "conserved" active site architecture.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Aug
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
21
pubmed:volume
46
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
9564-77
pubmed:dateRevised
2007-12-3
pubmed:meshHeading
pubmed-meshheading:17649980-Amino Acid Sequence, pubmed-meshheading:17649980-Aspartic Acid, pubmed-meshheading:17649980-Bacterial Proteins, pubmed-meshheading:17649980-Binding Sites, pubmed-meshheading:17649980-Catalysis, pubmed-meshheading:17649980-Conserved Sequence, pubmed-meshheading:17649980-Dicarboxylic Acids, pubmed-meshheading:17649980-Evolution, Molecular, pubmed-meshheading:17649980-Hydro-Lyases, pubmed-meshheading:17649980-Lysine, pubmed-meshheading:17649980-Molecular Conformation, pubmed-meshheading:17649980-Molecular Sequence Data, pubmed-meshheading:17649980-Mutation, pubmed-meshheading:17649980-Phosphopyruvate Hydratase, pubmed-meshheading:17649980-Protein Structure, Tertiary, pubmed-meshheading:17649980-Salmonella typhimurium, pubmed-meshheading:17649980-Substrate Specificity, pubmed-meshheading:17649980-Sugar Acids
pubmed:year
2007
pubmed:articleTitle
Evolution of enzymatic activities in the enolase superfamily: L-talarate/galactarate dehydratase from Salmonella typhimurium LT2.
pubmed:affiliation
Departments of Biochemistry and Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
pubmed:publicationType
Journal Article, Research Support, N.I.H., Extramural