Scientists at National Institutes of Health report research in anthrax
2007 NOV 19 -- Fresh data on anthrax are presented in the report 'Anthrax protective antigen cleavage and clearance from the blood of mice and rats.' "Bacillus anthracis protective antigen (PA) is an 83-kDa (PA83) protein that is cleaved to the 63-kDa protein (PA63) as an essential step in binding and internalizing lethal factor (LF). To assess in vivo receptor saturating PA concentrations, we injected mice with PA variants and measured the PA remaining in the blood at various times using PA83-and PA63-specific enzyme-linked immunosorbent assays," scientists in the United States report. "We found that both wild-type PA (WT-PA) and a receptor-binding-defective mutant (Ub-PA) were cleaved to PA63 independent of their ability to bind cells. This suggested a PA-acting protease activity in the blood. The protease cleaved PA at the furin cleavage sequence because furin site-modified PA mutants were not cleaved. Cleavage measured in vitro was leupeptin sensitive and dependent on calcium. Cell surface cleavage was important for toxin clearance, however, as Ub-PA and uncleavable PA mutants were cleared at slower rates than WT-PA. The cell binding-independent cleavage of PA was also verified by using Ub-PA (which is still cleaved) to rescue mice from toxin challenge by competitively binding circulating LF. This mutant was able to rescue mice even when given 12 h before toxin challenge. Its therapeutic ability was comparable to that of dominant-negative PA, which binds cells but does not allow LF translocation, and to the protection afforded through receptor clearance by WT-PA and uncleavable receptor binding-competent mutants. The PA cleavage and clearance observed in mice did not appear to have a role in the differential mouse susceptibility as it occurred similarly in lethal toxin (LT)-resistant DBA/2J and LT-sensitive BALB/cJ mice. Interestingly, PA63 was not found in LT-resistant or -sensitive rats and PA83 clearance was slower in rats than in mice," wrote M. Moayeri and colleagues, National Institutes of Health. The researchers concluded: "Finally, to determine the minimum amount of PA required in circulation for LT toxicity in mice, we administered time-separated injections of PA and LF and showed that lethality of LF for mice after PA was no longer measurable in circulation, suggesting active PA sequestration at tissue surfaces." Moayeri and colleagues published their study in Infection and Immunity (Anthrax protective antigen cleavage and clearance from the blood of mice and rats. Infection and Immunity, 2007;75(11):5175-84). For additional information, contact M. Moayeri, Laboratory of Bacterial Diseases, Building 33, Room 1W20, NIAID, National Institutes of Health, Bethesda, MD 20892-3202 USA.. The publisher's contact information for the journal Infection and Immunity is: American Society Microbiology, 1752 N St. NW, Washington, DC 20036-2904, USA. Keywords: United States, Bethesda, Anthrax, Enzymology, Protease. This article was prepared by Bioterrorism Week editors from staff and other reports. Copyright 2007, Bioterrorism Week via NewsRx.com.
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