Metal binding specificity of the MntABC permease of Neisseria gonorrhoeae and its influence on bacterial growth and interaction with cervical epithelial cells

Australian Bacterial Pathogenesis Program and Centre for Metals in Biology, School of Molecular and Microbial Sciences, The University of Queensland, St Lucia 4072, Australia; Centre for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital and the Department of Pediatrics, Ohio State University Columbus, Ohio 43205, USA; Department of Microbiology and Immunology, University of Iowa, Iowa City, Iowa 52242, USA

^* To whom correspondence should be addressed. Email: mcewan{at}uq.edu.au.

	Abstract

mntABC from Neisseria gonorrhoeae encodes an ABC permease which includes a periplasmic divalent cation-binding receptor protein of the Cluster IX family, encoded by mntC. Analysis of an mntC mutant showed that growth of N. gonorrhoeae could be stimulated by addition of either Manganese(II) or Zinc(II) ions, suggesting that the MntABC system could transport both ions. In contrast, growth of the mntAB mutant in liquid culture was only possible when the medium was supplemented with an antioxidant such as mannitol, consistent with the view that ion transport via MntABC is essential for protection of N. gonorrhoeae against oxidative stress. Using recombinant MntC, we determined that MntC binds Zn²⁺ and Mn²⁺ with almost equal affinity (K_d 0.1µM). Competition assays with the metallochromic zinc indicator, PAR showed that MntC binds Mn²⁺ and Zn²⁺ at the same binding site. Analysis of the N. gonorrhoeae genome showed that MntC is the only Mn/Zn metal binding receptor protein cluster IX in this bacterium, in contrast to the situation in many other bacteria which have systems with dedicated Mn and Zn binding proteins as part of distinctive ABC cassette permeases. Both the mntC and mntAB mutants had reduced intracellular survival in a human cervical epithelial cell model and showed reduced ability to form a biofilm. These data suggest that the MntABC transporter is of importance for survival of Neisseria gonorrhoeae in the human host.