ZOOCIN A AND ITS ASSOCIATED IMMUNITY FACTOR

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DESCRIPTION (Verbatim from Applicant's Abstract): The long-term goal of this research is to understand the control and transfer of information that allows some bacteria to produce toxic products to which they are not intrinsically resistant. The model systems being studied are lysostaphin, a plasmid-encoded staphylolytic glycylglycine endopeptidase produced by Staphylococcus simulans biovar staphylolyticus, which hydrolyzes the polyglycine cross bridges in the cell wall peptidoglycans of other staphylococci, and zoocin A, a chromosomally encoded streptococcolytic enzyme of unknown mechanism of action that is produced by Streptococcus equi subsp. zooepidemicus 4881. A comparison of the sequences of the genes for lysostaphin endopeptidase (end) and zoocin A (zooA) has revealed a high degree of similarity between these two enzymes; however, our preliminary investigations have revealed that zoocin A is most likely not simply an endopeptidase that hydrolyzes peptidoglycan cross bridges in susceptible streptococci. Both organisms carry resistance genes that also have a high degree of similarity (designated epr, for lysostaphin endopeptidase resistance and zif, for zoocin A immunity factor) immediately adjacent to the enzyme genes and oriented in the opposite direction to them. Both epr and zif have a high degree of similarity to femAB (factor essential for methicillin resistance) in staphylococci. The gene products for epr and femAB are known to be involved in the synthesis of cross bridges in the peptidoglycans of staphylococci; Epr specifies for the insertion of serines in these peptides whereas FemA and FemB specify for the insertion of glycines. Even though Zif is very similar to Epr, FemA, and FemB, our preliminary investigations have revealed that it is not involved in the biosynthesis of cross bridges. In addition, both end/epr and zooA/zif are bracketed by what appear to be transposable elements, suggesting that there may have been a horizontal transfer of DNA fragments containing these genes at some point in time. The specific aims of the proposed project are 1) to identify the site of action of zoocin A on the peptidoglycans of susceptible streptococci; 2) to identify the precise change made in streptococcal cell wall peptidoglycans by Zif and the cellular location of this protein; and 3) to determine if end/epr or zooA/zif can be transferred to other gram-positive organisms by natural mechanisms for genetic transfer.