ABSTRACT
In bacteria, the regulation of gene expression in response to changes in cell density is called quorum sensing. The autoinducer-2 production protein LuxS, is involved in a novel quorum-sensing system and is thought to catalyse the degradation of S-ribosylhomocysteine to homocysteine and the autoinducer molecule 4,5-dihydroxy-2,3-pentadione. The crystal structure of Bacillus subtilis LuxS has been determined at 1.2 A resolution, together with the binary complexes of LuxS with S-ribosylhomocysteine and homocysteine to 2.2 and 2.3 A resolution, respectively. These structures show that LuxS is a homodimer with an apparently novel fold based on an eight-stranded beta-barrel, flanked by six alpha-helices. Each active site contains a zinc ion coordinated by the conserved residues His54, His58 and Cys126, and includes residues from both subunits. S-ribosylhomocysteine binds in a deep pocket with the ribose moiety adjacent to the enzyme-bound zinc ion. Access to the active site appears to be restricted and possibly requires conformational changes in the protein involving the movement of residues 125-129 and those at the N terminus. The structure contains an oxidised cysteine residue in the active site whose role in the biological process of LuxS has not been determined. The autoinducer-2 signalling pathway has been linked to aspects of bacterial virulence and pathogenicity. The structural data on LuxS will provide opportunities for targeting this enzyme for the rational design of new antibiotics.
Subject(s)
Bacillus subtilis/enzymology , Bacterial Proteins/chemistry , Bacterial Proteins/metabolism , Amino Acid Sequence , Binding Sites , Carbon-Sulfur Lyases , Crystallography, X-Ray , Homocysteine/analogs & derivatives , Homocysteine/metabolism , Models, Molecular , Molecular Sequence Data , Protein Binding , Protein Structure, Quaternary , Protein Structure, Secondary , Selenomethionine/metabolism , Sequence Alignment , Zinc/metabolismSubject(s)
Antioxidants/pharmacology , Flavonoids/pharmacology , Neutrophils/physiology , Plant Extracts/pharmacology , Plants, Medicinal , Adult , Algeria , Flavonoids/chemistry , Flavonoids/isolation & purification , Humans , Hydrogen Peroxide/blood , Hypochlorous Acid/blood , In Vitro Techniques , Medicine, African Traditional , Neutrophils/drug effects , Plant Leaves , Reactive Oxygen Species/metabolism , Superoxides/blood , Tetradecanoylphorbol Acetate/pharmacologyABSTRACT
We have studied quantitatively the effect of the corepressor, S-adenosylmethionine (SAM), on the interaction between the E. coli methionine repressor, MetJ, and an idealised operator fragment, by recording measurements of surface plasmon resonance using a BIAcore instrument. We have recorded kinetic binding data in the presence of SAM, which carries a net positive charge, and two corepressor analogues, adenosylornithine (AO) and aza-SAM, which differ in the location of the atom carrying the positive charge. Our data support the hypothesis that the effect of the corepressor is electrostatic in origin. The difference in electrostatic interaction energy between the SAM- and AO-repressor-operator complexes of approximately 3.5 kJ/mol calculated from the known three-dimensional structure is within the range of our experimentally determined values of 2.8-4.3 kJ/mol. These results illustrate the potential of SPR measurements for studying protein-nucleic acid interactions.
