title: Characterization of the dihydrolipoamide dehydrogenase from Streptococcus pneumoniae and its role in pneumococcal infection.
abstract: In the present study, we have characterized the dihydrolipoamide dehydrogenase (DLDH) of Strepto-coccus pneumoniae and its role during pneumococcal infection. We have also demonstrated that a lack of DLDH results in a deficiency in alpha-galactoside metabolism and galactose transport. DLDH is an enzyme that is classically involved in the three-step conversion of 2-oxo acids to their respective acyl-CoA derivatives, but DLDH has also been shown to have other functions. The dldh gene was virtually identical in three pneumococcal strains examined. Besides the functional domains and motifs associated with this enzyme, analysis of the pneumococcal dldh gene sequence revealed the presence of an N-terminal lipoyl domain. DLDH-negative bacteria totally lacked DLDH activity, indicating that this gene encodes the only DLDH in S. pneumoniae. These DLDH-negative bacteria grew normally in vitro but were avirulent in sepsis and lung infection models in mice, indicating that DLDH activity is necessary for the survival of pneumococci within the host. The lack of virulence was not associated with a loss of 2-oxo acid dehydrogenase activity, as the wild-type pneumococcal strains did not contain activity of any of the known 2-oxo acid enzyme complexes. Instead, studies of carbohydrate utilization demonstrated that the DLDH-negative bacteria were impaired for alpha-galactoside and galactose metabolism. The DLDH mutants lost their ability to oxidize or grow with galactose or melibiose as sole carbon source and showed reduced oxidation and growth on raffinose or stachyose. The bacteria had an 85% reduction in alpha-galactosidase activity and showed virtually no transport of galactose into the cells, which can explain these phenotypic changes. The DLDH-negative bacteria produced only 50% of normal capsular polysaccharide, a phenotype that may be associated with impaired carbohydrate metabolism.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, BBRB-673 Box 10, 658 Bevill Building, 854 19th Street South, 35294, USA.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Smith
authors.forename: Hazeline
authors.initials: H
authors.lastname: Roche
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Trombe
authors.forename: David E
authors.initials: DE
authors.lastname: Briles
authors.forename: Anders
authors.initials: A
authors.lastname: Håkansson
mesh_terms: D000595:Amino Acid Sequence; D008058:Dihydrolipoamide Dehydrogenase / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D005798:Genes, Bacterial; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016366:Open Reading Frames; D010802:Phylogeny; D011008:Pneumococcal Infections / Q000382:microbiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D014169:Transformation, Bacterial; D000519:alpha-Galactosidase / Q000378:metabolism
chemical_list: D008058:Dihydrolipoamide Dehydrogenase; D000519:alpha-Galactosidase