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tcaA Inactivation Increases Glycopeptide Resistance in Staphylococcus aureus. Hideki Maki, 2004.The experimental deletion of the tcaRAB region has been shown to increase teicoplanin resistance in Staphylococcus aureus . By sequential genetic complementation of a tcaRAB mutant, we identified tcaA as the key gene within tcaRAB that is responsible for changes in glycopeptide resistance levels . Northern blot analysis of the tcaRAB region showed that the tcaA gene is expressed only weakly over the growth cycle and is strongly inducible by teicoplanin . Among some clinical isolates tested, glycopeptide-intermediate-resistant (GISA) strains Michigan and SA137/93G were found to have truncated tcaA genes . While the former carries a nucleotide insertion that creates a premature stop codon, the latter was found to harbor an IS256 insertion . Complementation of these two GISA strains with a functional tcaA allele reduced their levels of teicoplanin and vancomycin resistance five- to eightfold and twofold, respectively . The data presented here indicate that inactivation of tcaA contributes to and plays a relevant role in glycopeptide resistance in S . aureus clinical isolates . Structure-Function Analysis of Immunity Proteins of Pediocin-Like Bacteriocins: C-Terminal Parts of Immunity Proteins Are Involved in Specific Recognition of Cognate Bacteriocins. Line Johnsen, 2004.The immunity proteins of pediocin-like bacteriocins show a high degree of specificity with respect to the pediocin-like bacteriocin they recognize and confer immunity to . The aim of this study was to identify regions of the immunity proteins that are involved in this specific recognition . Six different hybrid immunity proteins were constructed from three different pediocin-like bacteriocin immunity proteins that have similar sequences but confer resistance to different bacteriocins . These hybrid immunity proteins were then tested for their ability to confer immunity to various pediocin-like bacteriocins . The specificities of the hybrid immunity proteins proved to be similar to those of the immunity proteins from which the C-terminal halves were derived, thus revealing that the C-terminal half of immunity proteins for pediocin-like bacteriocins contains a domain that is involved in specific recognition of the bacteriocins they confer immunity to . Moreover, the results also revealed that the effectiveness of an immunity protein is strain dependent and that its functionality thus depends in part on interplay with strain-dependent factors . To further investigate the structure-function relationship of these immunity proteins, the enterocin A and leucocin A immunity proteins (EntA-im and LeuA-im) were purified to homogeneity and structurally analyzed under various conditions by Circular dichroism (CD) spectroscopy . The results revealed that both immunity proteins are  -helical and well structured in an aqueous environment, the denaturing temperature being 78.5°C for EntA-im and 58.0°C for LeuA-im . The CD spectra also revealed that there was no further increase in the structuring or
-helical content when the immunity proteins were exposed to dodecylphosphocholine micelles or dioleoyl-L--phosphatidyl-DL-glycerol (DOPG) liposomes, indicating that the immunity proteins, in contrast to the bacteriocins, do not interact extensively with membranes . They may nevertheless be loosely associated with the membrane, possibly as peripheral membrane proteins, thus enabling them to interact with their cognate bacteriocin .
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