Use of a photoactivatable lipid to probe the topology of PA63 of Bacillus anthracis in lipid membranes

Functional reconstitution of protein ion channels into planar polymerizable phospholipid membranes

We demonstrate that polymerizable planar membranes permit reconstitution of protein ion channels formed by the bacterial toxins Staphylococcus aureus alpha-hemolysin (alphaHL) and Bacillus anthracis protective antigen 63. The alphaHL channel remained functional even after membrane polymerization. Surface pressure measurements suggest that the ease of forming membranes depends on membrane surface elasticity estimated from Langmuir-Blodgett monolayer pressure-area isotherms. The ability to stabilize nanoscale pores in robust ultrathin films may prove useful in single molecule sensing applications.

Structure and function of anthrax toxin

Anthrax toxin is a binary A-B toxin comprised of protective antigen (PA) and two enzymatic moieties, edema factor (EF) and lethal factor (LF). In the presence of a host cell-surface receptor, PA can mediate the delivery of EF and LF from the extracellular milieu into the host cell cytosol to effect toxicity. In this delivery, PA undergoes multiple structural changes--from a monomer to a heptameric prepore to a membrane-spanning heptameric pore. The catalytic factors also undergo dramatic structural changes as they unfold to allow for their translocation across the endosomal membrane and refold to preserve their catalytic activity within the cytosol. In addition to these gross structural changes, the intoxication mechanism depends on the ability of PA to form specific interactions with the host cell receptor, EF, and LF. This chapter presents a review of experiments probing these structural interactions and rearrangements in the hopes of gaining a molecular understanding of toxin action.

Role of residues constituting the 2beta1 strand of domain II in the biological activity of anthrax protective antigen

Anthrax toxin consists of three proteins, protective antigen, lethal factor and oedema factor. A proteolytically activated 63-kDa fragment of protective antigen binds lethal factor/oedema factor and translocates them into the cytosol. Domain II of protective antigen has been implicated in membrane insertion and channel formation. In the present study, alanine substitutions in 14 consecutive residues of the 2beta1 strand that are highly homologous to the putative membrane interacting segment of Clostridium perfringens iota-b toxin were generated and the effect on the biological activity of protective antigen studied. One of the mutants, Pro260Ala, showed considerably reduced toxicity in combination with lethal factor. The mutant also showed decreased membrane insertion and translocation of lethal factor into the cytosol. The data suggest that Pro260 is important for membrane insertion and translocation by protective antigen.

Current status of immunization against anthrax: old vaccines may be here to stay for a while

Anthrax vaccination has become a 'hot' topic. On the one hand, fears that Iraq holds secret caches of anthrax-based weaponry, that other countries may be developing or may have developed similar devices, or that hard-line groups may make their own anthrax-based devices for bioterrorist attacks have focused official attention on the need for means of protection, principally, though, for the military. On the other hand, the unsolved issues of the Gulf War illnesses have left elements of doubt in the minds of some as to the possible role of anthrax (among other) vaccines in this syndrome, and have drawn attention to the shortage of pre-clinical, clinical, pharmacological and safety data on the existing UK and US anthrax vaccines. In the middle are those hotly debating the US and Canadian policies of mandatory anthrax immunization for military personnel or, in the case of the UK policy of voluntary immunization, simply voting with their feet. Compounding matters have been the publicized failures of the US vaccine production facility and the less publicized UK problems of supply. Meanwhile, those in genuine at-risk occupations are left unsure whether, if they can get the vaccine at all, they really want it. Despite two decades of elegant science aimed at formulating alternative vaccines to overcome all the problems of efficacy, safety and supply, such an alternative is at least five years away, and the current status is that we must live with the old vaccines or not vaccinate.

Functional analysis of the carboxy-terminal domain of Bacillus anthracis protective antigen

Protective antigen (PA) is the common receptor-binding component of the two anthrax toxins. We investigated the involvement of the PA carboxy-terminal domain in the interaction of the protein with cells. A deletion resulting in removal of the entire carboxy-terminal domain of PA (PA608) or part of an exposed loop of 19 amino acids (703 to 722) present within this domain was introduced into the pag gene. PA608 did not induce the lethal-factor (LF)-mediated cytotoxic effect on macrophages because it did not bind to the receptor. In contrast, PA711- and PA705-harboring lethal toxins (9- and 16-amino-acid deletions in the loop, starting after positions 711 and 705, respectively) were 10 times less cytotoxic than wild-type PA. After cleavage by trypsin, the mutant PA proteins formed heptamers and bound LF. The capacity of PA711 and PA705 to interact with cells was 1/10 that of wild-type PA. In conclusion, truncation of the carboxy-terminal domain or deletions in the exposed loop resulted in PA that was less cytotoxic or nontoxic because the mutated proteins did not efficiently bind to the receptor.