Tachyzoites pretreated with Laz exhibited a 41% decrease in their ability to adhere to host cells (Fig

Tachyzoites pretreated with Laz exhibited a 41% decrease in their ability to adhere to host cells (Fig. 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. Apicomplexan protozoa include several members that present significant challenges to human health, such as (which causes malaria), (which causes cryptosporidiosis), and (which causes toxoplasmosis). can cause congenital birth defects in newborns of infected mothers and remains a serious complication in AIDS patients and other immunocompromised individuals (7, 9, 27). Additionally, is classified as a category B priority pathogen, relevant to biodefense research, by the National Institute for Allergy and Infectious Diseases (NIAID) (24). The toxicity associated with the primary treatment for recurring toxoplasmosis (pyrimethamine plus sulfadiazine) underscores the urgent need for novel strategies to combat tachyzoites, the invasive form of the parasite that produces the acute stage of infection, are covered with glycosylphosphatidylinositol-anchored surface antigen (SAG) proteins or SAG1-related sequence (SRS) proteins. The SRS proteins constitute a superfamily with at least 160 members, some of which are developmentally regulated (18). The large number of variant SRS proteins may explain why is capable of entering nearly any type of nucleated cell (13). With respect to the mechanism of host cell attachment, SAG3 has been demonstrated to bind with high affinity to sulfated proteoglycans (16). Crystallography studies of SAG1 (p30) show that a positively charged groove forms at the homodimer interface, the dimensions of which could accommodate negatively charged proteoglycans (13). Following attachment to the host cell, the parasite sequentially releases contents from specialized organelles (micronemes, rhoptries, and dense granules) that trigger Sacubitrilat invasion and establishment of the parasitophorous vacuole (3). SAG1, one of the more predominant SRS proteins on the parasite’s surface, is involved in host cell attachment and is a key virulence factor (19, 22). Antibodies to SAG1 also interfere with the parasite’s ability to invade host cells in vitro (20). SAG1 has been shown to be highly immunogenic, and anti-SAG1 antibodies protect mice infected with (17). Thus, therapies designed to target SAG1 in vivo are likely to have a significant benefit in controlling toxoplasmosis. Azurin (also referred to as Paz) is a 128-amino-acid periplasmic protein produced by Icam1 the bacterium that has antimicrobial activity (4). Azurin is a redox protein initially believed only to serve as an electron donor to nitrite reductase during anaerobic respiration, but no such obligatory role has been confirmed (26). and other members of the gonococci/meningococci produce an azurin-like protein called Laz on their surface. Laz has an additional 39-amino-acid peptide at its N terminus called an H.8 epitope (15). Azurin and Laz are collectively referred to as azurin proteins in this report. Azurin proteins are members of a family of copper-containing proteins known as cupredoxins, which are involved in Sacubitrilat electron transfer. Recently it was documented that portions of azurin proteins share structural similarities with a wide variety of other proteins, including variable domains of immunoglobulins and mammalian cell surface receptors and/or ligands. For example, azurin shows structural similarity to the Fab fragment that binds the merozoite surface protein I (MSP1) and binds to CD4, which acts as a receptor for the human immudeficiency virus type 1 (HIV-1) envelope glycoprotein gp120. Consequently, azurin proteins interfere with the invasion of HIV-1 and reduce parasitemia of by binding to envelope or surface proteins, respectively (4). This phenomenon has led to a hypothesis that azurin proteins may play dual roles in pathogenic bacteria, one of which is to serve as a versatile weapon against competing microbes attempting to invade the same host Sacubitrilat (8). In this study, we report the effects of azurin proteins on and that the mechanism of action involves interference with SAG1-mediated attachment to host.

---