title: A Toxoplasma gondii rhoptry protein associated with host cell penetration has unusual charge asymmetry.
abstract: The monoclonal antibody Tg49 both recognizes a Toxoplasma gondii rhoptry protein (ROP1) and inhibits penetration enhancing factor. The latter is a proteinaceous factor found in Toxoplasma lysates or conditioned media that increases the efficiency with which parasites invade host cells. Tg49 was used to screen a lambda gt11 cDNA library and the clone obtained was identified as the cognate gene for ROP1 by several criteria: (1) recombinant protein reacted with the monoclonal; (2) antiserum against the recombinant reacted with the same bands on Western blots as did Tg49; and (3) antiserum against the recombinant recognized a protein in the rhoptries. The ROP1 gene is a single copy gene with a message of approximately 2.1 kb. The predicted polypeptide sequence of ROP1 shows an unusual charge and amino acid asymmetry. There is a highly acidic, proline-rich domain in the amino-terminal portion of the predicted protein, followed by a strongly basic carboxy-terminal domain. An octapeptide repeat is found almost midway through the peptide sequence toward the end of the acidic domain. The ROP1 gene was expressed in a bacterial system, and the resulting polypeptide exhibited anomalous migration on polyacrylamide gel electrophoresis. Given that Tg49 inhibits penetration enhancing factor, it seems likely that the ROP1 protein is a component of that factor, and that the unusual sequence of this protein plays some role in host cell penetration by T. gondii.
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, CA 94305-5402.
authors.forename: P N
authors.initials: PN
authors.lastname: Ossorio
authors.forename: J D
authors.initials: JD
authors.lastname: Schwartzman
authors.forename: J C
authors.initials: JC
authors.lastname: Boothroyd
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000953:Antigens, Protozoan / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D015139:Blotting, Southern; D015153:Blotting, Western; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D011993:Recombinant Fusion Proteins; D015183:Restriction Mapping; D014122:Toxoplasma / Q000235:genetics*
chemical_list: D000911:Antibodies, Monoclonal; D000953:Antigens, Protozoan; D016054:DNA, Protozoan; D008565:Membrane Proteins; D015800:Protozoan Proteins; C117001:ROP 1 protein, Toxoplasma gondii; D011993:Recombinant Fusion Proteins; C065352:rhoptry associated protein, Plasmodium