Solution structure of a putative FKBP-type peptidyl-propyl cis–trans isomerase from Giardia lamblia

Abstract

The FK506 Binding Protein (FKBP) super-family was named for the ability of these proteins to bind to the immunosuppressive drug FK506, a 23-member macrolide lactone. Immunosuppression is achieved when the proteinFK506 complex binds to calcineurin to form a larger complex that blocks signal transduction in the T-lymphocyte transduction pathway (Gothel and Marahiel 1999). FKBP proteins also have peptidyl-proline cis–trans isomerases (PPIase) activity that catalyzes the interconversion of the peptidyl-prolyl imide bond between the cis and trans configuration in peptide and protein substrates (Gothel and Marahiel 1999). The isomerase activity is unrelated to the immunosuppressive effects when bound to FK506, but, is essential for the proper folding of many proteins and a number of PPIases act as chaperones. Because proper protein folding is often necessary for proper biochemical function, FKBP proteins are indirectly associated with many diverse biologically processes including trafficking, cell-cycle regulation, development, and signal transduction (Gothel and Marahiel 1999). It has been observed that the parasite Trypanosoma cruzi secretes a FKBP-type protein upon infecting its host, leading to the suggestion that some parasites may use these proteins as virulence factors (Moro et al. 1995). Cultures of the parasite responsible for malaria, Plasmodium falciparum, are sensitive to FK506 (Bell et al. 1994). Regardless of the potential role of FKBP-type proteins as parasite virulence factors, the many critical biologically functions dependent on FKBP-type proteins makes this super-family of proteins good drug targets (Moro et al. 1995; Alag et al. 2010). The most common parasitic protist in the United States is Giardia lamblia (Krappus et al. 1994): the etiological agent responsible for giardiasis, an infection of the small intestines that often causes diarrhea. While giardiasis is generally not life-threatening, in developing countries this enteric protozoan parasite contributes to malnutrition and underperformance in school, and consequently, has been added to the ‘‘Neglected Disease Initiative’’ list by the World Health Organization (Savioli et al. 2006). Recently, the G. lamblia genome was sequenced (Morrison et al. 2007) and among the 6,470 genes encoded in the five chromosomes is a putative, 109-residue FKBP-type PPIase, Gl-FKBP. To assist structure-based design of a more palatable, single-dose treatment for giardiasis targeting GlFKBP, we used NMR-based methods to determine its structure in solution. The structure of Gl-FKBP and the G. W. Buchko S. N. Hewitt W. C. Van Voorhis P. J. Myler Seattle Structural Genomics Center for Infectious Disease, Seattle, WA, USA