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Infection and Immunity, August 2004, p. 4351-4356, Vol. 72, No. 8
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.8.4351-4356.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Cleavage of Human Transferrin by Porphyromonas gingivalis Gingipains Promotes Growth and Formation of Hydroxyl Radicals

Groupe de Recherche en Écologie Buccale and Faculté de Médecine Dentaire, Université Laval, Québec, Canada G1K 7P4,¹ Department of Internal Medicine and Research Service, VA Medical Center and Roy G. and Lucille A. Cartver College of Medicine of The University of Iowa, Iowa City, Iowa 52246,² Department of Microbiology, School of Dentistry, Nagasaki University, Sakamoto 1-7-1, Nagasaki 852-8588, Japan³

Received 14 January 2004/ Returned for modification 16 February 2004/ Accepted 10 April 2004

Porphyromonas gingivalis, a gram-negative anaerobic bacterium associated with active lesions of chronic periodontitis, produces several proteinases which are presumably involved in host colonization, perturbation of the immune system, and tissue destruction. The aims of this study were to investigate the degradation of human transferrin by gingipain cysteine proteinases of P. gingivalis and to demonstrate the production of toxic hydroxyl radicals (HO^·) catalyzed by the iron-containing transferrin fragments generated or by release of iron itself. Analysis by polyacrylamide gel electrophoresis and Western immunoblotting showed that preparations of Arg- and Lys-gingipains of P. gingivalis cleave transferrin (iron-free and iron-saturated forms) into fragments of various sizes. Interestingly, gingival crevicular fluid samples from diseased periodontal sites but not samples from healthy periodontal sites contained fragments of transferrin. By using ⁵⁵Fe-transferrin, it was found that degradation by P. gingivalis gingipains resulted in the production of free iron, as well as iron bound to lower-molecular-mass fragments. Subsequent to the degradation of transferrin, bacterial cells assimilated intracellularly the radiolabeled iron. Growth of P. gingivalis ATCC 33277, but not growth of an Arg-gingipain- and Lys-gingipain-deficient mutant, was possible in a chemically defined medium containing 30% iron-saturated transferrin as the only source of iron and peptides, suggesting that gingipains play a critical role in the acquisition of essential growth nutrients. Finally, the transferrin degradation products generated by Arg-gingipains A and B were capable of catalyzing the formation of HO^·, as determined by a hypoxanthine/xanthine oxidase system and spin trapping-electron paramagnetic resonance spectrometry. Our study indicates that P. gingivalis gingipains degrade human transferrin, providing sources of iron and peptides. The iron-containing transferrin fragments or the release of iron itself may contribute to tissue destruction by catalyzing the formation of toxic HO^·.

Editor: W. A. Petri, Jr.

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