Lactoferrin Inhibits Porphyromonas gingivalis Proteinases and Has Sustained Biofilm Inhibitory Activity

Abstract

ABSTRACTPorphyromonas gingivalisis a bacterial pathogen associated with chronic periodontitis that results in destruction of the tooth's supporting tissues. The major virulence determinants ofP. gingivalisare its cell surface Arg- and Lys-specific cysteine proteinases, RgpA/B and Kgp. Lactoferrin (LF), an 80-kDa iron-binding glycoprotein found in saliva and gingival crevicular fluid, is believed to play an important role in innate immunity. In this study, bovine milk LF displayed proteinase inhibitory activity againstP. gingivaliswhole cells, significantly inhibiting both Arg- and Lys-specific proteolytic activities. LF inhibited the Arg-specific activity of purified RgpB, which lacks adhesin domains, and also inhibited the same activity of the RgpA/Kgp proteinase-adhesin complexes in a time-dependent manner, with a first-order inactivation rate constant (kinact) of 0.023 min−1and an inhibitor affinity constant (KI) of 5.02 μM. LF inhibitedP. gingivalisbiofilm formation by >80% at concentrations above 0.625 μM. LF was relatively resistant to hydrolysis byP. gingivaliscells but was cleaved into two major polypeptides (53 and 33 kDa) at R284to S285, as determined by in-source decay mass spectrometry; however, these polypeptides remained associated with each other and retained inhibitory activity. The biofilm inhibitory activity of LF againstP. gingivaliswas not attributed to direct antibacterial activity, as LF displayed little growth inhibitory activity against planktonic cells. As the known RgpA/B and Kgp inhibitorN-α-p-tosyl-l-lysine chloromethylketone also inhibitedP. gingivalisbiofilm formation, the antibiofilm effect of LF may at least in part be attributable to its antiproteinase activity.