ABSTRACT
To investigate the effect of the autoinducer AI-2 on protein expression in Neisseria meningitidis, a luxS mutant of strain MC58 was grown in the presence and absence of in vitro-produced AI-2, and differential protein expression was assessed by two-dimensional differential gel electrophoresis. N. meningitidis did not show a global response to AI-2 signaling activity.
Subject(s)
Bacterial Proteins/analysis , Homoserine/analogs & derivatives , Homoserine/physiology , Neisseria meningitidis/metabolism , Bacterial Proteins/physiology , Carbon-Sulfur Lyases , Electrophoresis, Gel, Two-Dimensional , Lactones , Proteomics , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
Cell-cell communication in bacteria is accomplished through the exchange of extracellular signalling molecules called autoinducers. This process, termed quorum sensing, allows bacterial populations to coordinate gene expression. Community cooperation probably enhances the effectiveness of processes such as bioluminescence, virulence factor expression, antibiotic production and biofilm development. Unlike other autoinducers, which are specific to a particular species of bacteria, a recently discovered autoinducer (AI-2) is produced by a large number of bacterial species. AI-2 has been proposed to serve as a 'universal' signal for inter-species communication. The chemical identity of AI-2 has, however, proved elusive. Here we present the crystal structure of an AI-2 sensor protein, LuxP, in a complex with autoinducer. The bound ligand is a furanosyl borate diester that bears no resemblance to previously characterized autoinducers. Our findings suggest that addition of naturally occurring borate to an AI-2 precursor generates active AI-2. Furthermore, they indicate a potential biological role for boron, an element required by a number of organisms but for unknown reasons.
Subject(s)
Borates/chemistry , Boron/chemistry , Bridged Bicyclo Compounds, Heterocyclic/chemistry , Homoserine/analogs & derivatives , Homoserine/chemistry , Lactones/chemistry , Signal Transduction , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Bacterial Proteins/physiology , Boron/physiology , Crystallography, X-Ray , Escherichia coli , Homoserine/physiology , Models, Molecular , Recombinant Fusion Proteins/chemistry , Vibrio/chemistry , Vibrio/physiologyABSTRACT
A sorbitol dehydrogenase (SDH; L-iditol:NAD+ 2-oxidoreductase; EC 1.1.1.14) was isolated from the phototrophic bacterium Rhodobacter sphaeroides strain M22, a transposon mutant of R. sphaeroides Si4 with the transposon inserted in the mannitol dehydrogenase (MDH) gene. SDH was purified 470-fold to apparent homogeneity by ammonium sulfate precipitation, chromatography on Phenyl-Sepharose, Q-Sepharose and Matrex Gel Red-A, and by gel filtration on Superdex 200. The relative molecular mass (M(r)) of the native SDH was 61000 as calculated from its Stokes' radius (rs = 3.5 nm) and sedimentation coefficient (S20,w = 4.23S). SDS-PAGE resulted in one single band representing a polypeptide with a M(r) of 29,000, indicating that the native protein is a dimer. The isoelectric point of SDH was determined to be pH 4.8. The enzyme was specific for NAD+ and catalysed the oxidation of D-glucitol (sorbitol) to D-fructose, galactitol to D-tagatose and of L-iditol. The apparent Km values were NAD+, 0.06 mM; D-glucitol, 6.2 mM; galactitol, 1.5 mM; NADH, 0.13 mM; D-fructose, 160 mM; and D-tagatose, 13 mM. The pH-optimum of substrate oxidation was 11.0 and that of substrate reduction 6.0-7.2. It was demonstrated that SDH is expressed in the wild-type strain R. sphaeroides Si4 together with MDH during growth on D-glucitol. Forty-four amino acids of the SDH N terminus were sequenced. This sequence exhibited 45-55% identity to the N-terminal sequence of 10 enzymes belonging to the short-chain alcohol dehydrogenase family.
