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Applied and Environmental Microbiology, October 2009, p. 6205-6210, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.01011-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Zif, the Zoocin A Immunity Factor, Is a FemABX-Like Immunity Protein with a Novel Mode of Action{triangledown}

Shaw R. Gargis,1 Amy S. Gargis,1 Harry E. Heath,1 Lucie S. Heath,1 Paul A. LeBlanc,1 Maria M. Senn,2 Brigitte Berger-Bächi,2 Robin S. Simmonds,3 and Gary L. Sloan1*

Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama,1 Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland,2 Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand3

Received 4 May 2009/ Accepted 7 August 2009

Producer cell immunity to the streptococcolytic enzyme zoocin A, which is a D-alanyl-L-alanine endopeptidase, is due to Zif, the zoocin A immunity factor. Zif has high degrees of similarity to MurM and MurN (members of the FemABX family of proteins), which are responsible for the addition of amino acids to cross bridges during peptidoglycan synthesis in streptococci. In this study, purified peptidoglycans from strains with and without zif were compared to determine how Zif modifies the peptidoglycan layer to cause resistance to zoocin A. The peptidoglycan from each strain was hydrolyzed using the streptococcolytic phage lysin B30, and the resulting muropeptides were separated by reverse-phase high-pressure liquid chromatography, labeled with 4-sulfophenyl isothiocyanate, and analyzed by tandem mass spectrometry in the negative-ion mode. It was determined that Zif alters the peptidoglycan by increasing the proportion of cross bridges containing three L-alanines instead of two. This modification decreased binding of the recombinant target recognition domain of zoocin A to peptidoglycan. Zif-modified peptidoglycan also was less susceptible to hydrolysis by the recombinant catalytic domain of zoocin A. Thus, Zif is a novel FemABX-like immunity factor because it provides resistance to a bacteriolytic endopeptidase by lengthening the peptidoglycan cross bridge rather than by causing an amino acid substitution.

* Corresponding author. Mailing address: Department of Biological Sciences, Box 870334, The University of Alabama, Tuscaloosa, AL 35487-0334. Phone: (205) 348-8444. Fax: (205) 348-5976. E-mail: gsloan{at}bama.ua.edu

{triangledown} Published ahead of print on 14 August 2009.

Applied and Environmental Microbiology, October 2009, p. 6205-6210, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.01011-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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