Neisseria gonorrhoeae porin, P.IB, causes release of ATP from yeast actin

Neisserial porins may play a role in the invasion of the host cell by the bacterium. The protein translocates to the host cell membrane and then to the cytosol during the invasive process, and we have shown it interacts with actin in vitro. Here, we have examined the nucleotide-dependence of the interaction of Neisseria porin, P.IB, with fluorescently labeled yeast G actin. Increasing free ATP between 0 to 0.5 mM retards complex formation between the two proteins. The ATP effect probably results from binding of the nucleotide to actin rather than to porin. Complex formation results in a biphasic release of bound nucleoside triphosphate from actin in the absence of free nucleotide at a rate slower than that of complex formation, but it does not induce hydrolysis of the actin-bound nucleotide. ATP prevents the porin-induced distortion of F-actin structure, and addition of ATP to the complex formed in the absence of free nucleotide induces actin polymerization indicating that P.IB stabilizes nucleotide-free G-actin. Our results suggest that P.IB causes an actin conformation change leading to the production of a polymerization-competent nucleotide-free protein.