Abstract
BackgroundPrevotella intermedia is a Gram-negative black-pigmenting oral anaerobe associated with periodontitis in humans, and has a haem requirement for growth, survival and virulence. It produces an iron porphyrin-containing pigment comprising monomeric iron (III) protoporphyrin IX (Fe(III)PPIX.OH; haematin). The bacterium expresses a 90-kDa cysteine protease termed interpain A (InpA) which both oxidizes and subsequently degrades haemoglobin, releasing haem. However, it is not known whether the enzyme may play a role in degrading other haem-carrying plasma proteins present in the gingival sulcus or periodontal pocket from which to derive haem. This study evaluated the ability of InpA to degrade apo- and haem-complexed albumin.ResultsAlbumin breakdown was examined over a range of pH and in the presence of reducing agent; conditions which prevail in sub- and supra-gingival plaque. InpA digested haemalbumin more efficiently than apoalbumin, especially under reducing conditions at pH 7.5. Under these conditions InpA was able to substantially degrade the albumin component of whole human plasma.ConclusionsThe data point to InpA as an efficient “albuminase” with the ability to degrade the minor fraction of haem-bound albumin in plasma. InpA may thus contribute significantly to haem acquisition by P. intermedia under conditions of low redox potential and higher pH in the inflamed gingival crevice and diseased periodontal pocket where haem availability is tightly controlled by the host.
Highlights
Prevotella intermedia is a Gram-negative black-pigmenting oral anaerobe associated with periodontitis in humans, and has a haem requirement for growth, survival and virulence
Given that albumin represents an important source of haem under conditions of haem scarcity, we examined the ability of interpain A (InpA) to degrade albumin in both its apo- and haem-liganded forms under conditions which may prevail in the primary habitats of this bacterium, the inflamed gingival sulcus and diseased periodontal pocket
Since the redox potential of diseased periodontal pockets can be as low as −300 mV [20] and that P. intermedia may experience wide fluctuations of pH within dental plaque, it was considered appropriate to examine the effect of these two variables on the activity of InpA
Summary
Prevotella intermedia is a Gram-negative black-pigmenting oral anaerobe associated with periodontitis in humans, and has a haem requirement for growth, survival and virulence It produces an iron porphyrincontaining pigment comprising monomeric iron (III) protoporphyrin IX (Fe(III)PPIX.OH; haematin). Members of the genus Prevotella are associated with periodontal diseases in humans and other animals [1] They have a growth requirement for iron protoporphyrin IX, and display a characteristic black-pigmenting phenotype due to cell-surface accumulation of haem (iron(III) protoporphyrin IX) in the monomeric form (Fe(III)PPIX.OH, haematin), derived via the breakdown of haemoglobin [2]. In healthy or minimally inflamed gingival crevices, in the absence of overt bleeding (and haemoglobin), their survival and growth may depend on haemalbumin and haem-haemopexin as primary haem sources These proteins normally sequester any circulating free haem and transport it to the liver [4, 5], limiting its bioavailability to invading micro-organisms. Albumin has a 75-fold lower affinity for haem compared to haemopexin [9], its haem sequestering capability is compensated by its 40-80-fold greater
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