Some pathogenic bacteria produce factors that have evolved a capacity to neutralize competing microbes. The
cupredoxin family
protein azurin, produced by Pseudomonas aeruginosa, exhibits a remarkable ability to impede invasion of a number of diverse intracellular pathogens, including the human AIDS virus human immunodeficiency virus type 1 and the protozoan parasite Plasmodium falciparum (which causes
malaria). Here we report that
azurin and an
azurin-like
protein (Laz) from gonococci/meningococci have activity against Toxoplasma, an apicomplexan parasite that causes
opportunistic infection in immunocompromised individuals. We demonstrate that the mechanism of action for Laz involves interfering with the ability of Toxoplasma to adhere to host cells. Computer structural analysis reveals that
azurin shares structural features with the predominant
surface antigen SAG1, which is known to play an important role in parasite attachment. Interestingly,
azurin also has structural similarities to a
monoclonal antibody to SAG1. Surface plasmon resonance binding studies validate that SAG1 interacts strongly with Laz and, to lesser extent,
azurin. Moreover, Toxoplasma mutants lacking SAG1 are not as susceptible to the growth-inhibitory effects of Laz. Collectively, our data show that Toxoplasma adhesion can be significantly impaired by Laz, and to some extent by
azurin, via interactions with SAG1. These observations indicate that Laz can serve as an important tool in the study of host-pathogen interactions and is worthy of further study for development into potential therapeutic agents.