Two distinct ferritin-like molecules in P . aeruginosa : The product of the bfrA gene is a bacterial ferritin ( FtnA ) not a bacterioferritin ( Bfr ) †

Two distinct types of ferritin-like molecules often coexist in bacteria, the heme binding bacterioferritins (Bfr) and the non-heme binding bacterial ferritins (Ftn). The early isolation of a ferritin-like molecule from P. aeruginosa suggested the possibility of a bacterioferritin assembled from two different subunits [Moore, G. R. , Kadir, F. H. , Al-Massad, F. K. , Le Brun, N. E. , Thomson, A. J., Greenwood, C. , Keen, J. N. and Findlay, J. B. C. (1994) Biochem. J. 304, 493– 497]. Subsequent studies demonstrated the presence of two genes coding for ferritin-like molecules in P. aeruginosa, designated bfrA and bfrB, and suggested that two distinct bacterioferritins may coexist [Ma, J.-F. , Ochsner, U. A. , Klotz, M. G, Nanayakkara, V. K. , Howell, M. L. , Johnson, Z. , Posey, J. E. , Vasil, M. L. , Monaco, J. J., and Hassett, D. J. (1999) J. Bacteriol. 181, 3730–3742]. In this report we present structural evidence demonstrating that the product of the bfrA gene is a ferritin-like molecule not capable of binding heme which harbors a catalytically active ferroxidase center with structural properties similar to those characteristic of bacterial and archaeal Ftns and clearly distinct from the ferroxidase center typical of Bfrs. Consequently, the product of the bfrA gene in P. aeruginosa is a bacterial ferritin, which we propose should be termed Pa FtnA. These results, together with the previous characterization of the product of the bfrB gene as a genuine bacterioferritin (Pa BfrB) [Weeratunga, S. J., Lovell, S. , Yao, H. , Battaile, K. P., Fischer, C. J., Gee, C. E. , and Rivera, M. (2010) Biochemistry 49. 1160– 1175] indicate the coexistence of a bacterial ferritin (Pa FtnA) and a bacterioferritin (Pa BfrB) in P. aeruginosa. In agreement with this idea, we also obtained evidence demonstrating that release †This work was supported by grants from the National Science Foundation (MCB-0818488), the National Institute of Health, GM-50503 and P20 RR-17708 from the National Center for Research Resources. €Coordinates and crystallographic structure factors for the distinct Pa FtnA structures have been deposited in the protein data bank under accession codes 3R2O (as isolated pH 6.0), 3R2K (as isolated pH 7.5), 3R2H (as isolated pH 10.5), 3R2R (Fe soaked, pH 6.0), 3R2L (Fe soaked, pH 7.5), 3R2S (double soaked, pH 6.0) and 3R2M (double soaked, pH 7.5). *Corresponding author: Mario Rivera, Ralph N. Adams Institute for Bioanalytical Chemistry & Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS 66047. Telephone: 785-864-4936; Fax: 785-864-1916; mrivera@ku.edu. SUPPORTING INFORMATION Amino acid sequence of the protein coded by the P. aeruginosa bfrA gene (Pa FtnA) aligned against the amino acid sequences of bacterioferritins of known structure; 2Fo-Fc electron density maps of the ferroxidase center ligands of Pa FtnA Fe soaked and double soaked; conformational changes in the Pa FtnA ferroxidase center upon binding iron; anomalous difference map showing sulfate in a 3-fold pore. This material is available free of charge via the Internet at http://pubs.acs. org NIH Public Access