title: A novel class of dual-family immunophilins.
abstract: Immunophilins are protein chaperones with peptidylprolyl isomerase activity that belong to one of two large families, the cyclosporin-binding cyclophilins (CyPs) and the FK506-binding proteins (FKBPs). Each family displays characteristic and conserved sequence features that differ between the two families. We report a novel group of dual-family immunophilins that contain both CyP and FKBP domains for which we propose the name FCBP (FK506- and cyclosporin-binding protein). The FCBP of Toxoplasma gondii, a protozoan parasite, contained N-terminal FKBP and C-terminal CyP domains joined by tetratricopeptide repeats. Structure-function analysis revealed that both domains were functional and exhibited family-specific drug sensitivity. The individual domains of FCBP inhibited calcineurin (protein phosphatase 2B) in the presence of the appropriate drugs. In binding studies, FCBP recruited calcineurin in the presence of FK506 and a putative target of rapamycin homolog in the presence of rapamycin. Two additional FCBP sequences in Flavobacterium and one in Treponema (spirochete) were also identified in which the CyP and FKBP domains were in the reverse order. T. gondii growth was inhibited by cyclosporin and FK506 in a moderately synergistic manner. The knockdown of FCBP by RNA interference revealed its essentiality for T. gondii growth. Clearly, the FCBPs are novel chaperones and potential targets of multiple immunosuppressant drugs.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of South Alabama, College of Medicine, Mobile, Alabama 36688-0002, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Adams
authors.forename: Alla
authors.initials: A
authors.lastname: Musiyenko
authors.forename: Rajinder
authors.initials: R
authors.lastname: Kumar
authors.forename: Sailen
authors.initials: S
authors.lastname: Barik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019703:Calcineurin / Q000737:chemistry; D002417:Cattle; D016572:Cyclosporine / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D005417:Flavobacterium / Q000378:metabolism; D006801:Humans; D020104:Immunophilins / Q000737:chemistry* / Q000145:classification*; D007166:Immunosuppressive Agents / Q000737:chemistry / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D019696:Peptidylprolyl Isomerase / Q000737:chemistry; D010641:Phenotype; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D020123:Sirolimus / Q000737:chemistry; D013329:Structure-Activity Relationship; D016559:Tacrolimus / Q000737:chemistry / Q000494:pharmacology; D013997:Time Factors; D014122:Toxoplasma / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D007166:Immunosuppressive Agents; D018832:Molecular Chaperones; D010455:Peptides; D011994:Recombinant Proteins; D016572:Cyclosporine; D019703:Calcineurin; D020104:Immunophilins; D019696:Peptidylprolyl Isomerase; D020123:Sirolimus; D016559:Tacrolimus