|
|
|
|
|
|
Structural and Functional Differences in Two Cyclic Bacteriocins with the Same Sequences Produced by Lactobacilli. Yasushi Kawai, 2004.Lactobacillus gasseri LA39 and L . reuteri LA6 isolated from feces of the same human infant were found to produce similar cyclic bacteriocins (named gassericin A and reutericin 6, respectively) that cannot be distinguished by molecular weights or primary amino acid sequences . However, reutericin 6 has a narrower spectrum than gassericin A . In this study, gassericin A inhibited the growth of L . reuteri LA6, but reutericin 6 did not inhibit the growth of L . gasseri LA39 . Both bacteriocins caused potassium ion efflux from indicator cells and liposomes, but the amounts of efflux and patterns of action were different . Although circular dichroism spectra of purified bacteriocins revealed that both antibacterial peptides are composed mainly of  -helices, the spectra of the bacteriocins did not coincide . The results of D- and L-amino acid composition analysis showed that two residues and one residue of D-Ala were detected among 18 Ala residues of gassericin A and reutericin 6, respectively . These findings suggest that the different D-alanine contents of the bacteriocins may cause the differences in modes of action, amounts of potassium ion efflux, and secondary structures . This is the first report that characteristics of native bacteriocins produced by wild lactobacillus strains having the same structural genes are influenced by a difference in D-amino acid contents in the molecules .
Mutational Analysis of the Escherichia coli PhoQ Sensor Kinase: Differences with the Salmonella enterica Serovar Typhimurium PhoQ Protein and in the Mechanism of Mg2+ and Ca2+ Sensing. Adam G. Regelmann, 2002.The PhoP-PhoQ two-component system plays a role in Mg2+ homeostasis and/or the virulence properties of a number of bacterial species . A Salmonella enterica serovar Typhimurium PhoQ sensor kinase mutant, in which the threonine at residue 48 in the periplasmic sensor domain is changed to an isoleucine, was shown previously to result in elevated expression of PhoP-activated genes and to affect mouse virulence, epithelial cell invasion, and sensitivity to macrophage killing . We characterized a complete set of proteins having amino acid substitutions at position 48 in the closely related Escherichia coli PhoQ protein . Numerous mutant proteins having amino acid substitutions with side chains of various sizes and characters displayed signaling phenotypes similar to that of the wild-type protein, indicating that interactions mediated by the wild-type threonine side chain are not required for normal protein function . Changes to amino acids with aromatic side chains had little impact on signaling in response to extracellular Mg2+ but resulted in reduced sensitivity to extracellular Ca2+, suggesting that the mechanisms of signal transduction in response to these two divalent cations are different . Surprisingly, the Ile48 protein displayed a defective phenotype rather than the hyperactive phenotype seen with the S . enterica serovar Typhimurium protein . We also describe a mutant PhoQ protein lacking the extracellular sensor domain with a defect in the ability to activate PhoP . The defect does not appear to be due to reduced autokinase activity but rather appears to be due to an effect on the stability of the aspartyl-phosphate bond of phospho-PhoP . Site-Directed Mutagenesis Studies of Selected Motif and Charged Residues and of Cysteines of the Multifunctional Tetracycline Efflux Protein Tet(L). Jie Jin, 2002.All of the transmembrane glutamates of Tet(L) are essential for tetracycline (TET) resistance, and E397 has been shown to be essential for all catalytic modes, i.e., TET-Me2+ and Na+ efflux and K+ uptake . Loop residues D74 and G70 are essential for TET flux but not for Na+ or K+ flux . A cysteineless Tet(L) protein exhibits all activities . Role of Capsular Colanic Acid in Adhesion of Uropathogenic Escherichia coli. Andrea Hanna, 2003.Urinary tract infections are the most common urologic disease in the United States and one of the most common bacterial infections of any organ system . Biofilms persist in the urinary tract and on catheter surfaces because biofilm microorganisms are resistant to host defense mechanisms and antibiotic therapy . The first step in the establishment of biofilm infections is bacterial adhesion; preventing bacterial adhesion represents a promising method of controlling biofilms . Evidence suggests that capsular polysaccharides play a role in adhesion and pathogenicity . This study focuses on the role of physiochemical and specific binding interactions during adhesion of colanic acid exopolysaccharide mutant strains . Bacterial adhesion was evaluated for isogenic uropathogenic Escherichia coli strains that differed in colanic acid expression . The atomic force microscope (AFM) was used to directly measure the reversible physiochemical and specific binding interactions between bacterial strains and various substrates as bacteria initially approach the interface . AFM results indicate that electrostatic interactions were not solely responsible for the repulsive forces between the colanic acid mutant strains and hydrophilic substrates . Moreover, hydrophobic interactions were not found to play a significant role in adhesion of the colanic acid mutant strains . Adhesion was also evaluated by parallel-plate flow cell studies in comparison to AFM force measurements to demonstrate that prolonged incubation times alter bacterial adhesion . Results from this study demonstrate that the capsular polysaccharide colanic acid does not enhance bacterial adhesion but rather blocks the establishment of specific binding as well as time-dependent interactions between uropathogenic E . coli and inert substrates .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
