-transferases (GSTs) are detoxifying enzymes that appear across a wide range of aerobic organisms, including bacteria, fungi, plants and mammals. This enzyme superfamily conjugates toxins with glutathione and the conjugate is then eliminated from the organism. Trimeric membrane-bound and dimeric cytosolic GSTs have been described, although they do not appear to share sequence or structural similarities (Hayes & Pulford, 1995
). All cytosolic GSTs share a common fold (βαβαββα, related to thioredoxin) and they are divided into a number of different classes (α, μ, ω, π, θ, ζ etc
.) based on sequence analysis (Snyder & Maddison, 1997
). Crystal structures have been determined for all major classes of GSTs (Dirr et al.
; Sheehan et al.
). These structures reveal a G-site where glutathione binds and an H-site where the hydrophobic substrate binds. Many organisms contain multiple GST isoforms that recognize different or occasionally overlapping substrates (Mannervik et al.
). Human π-class GSTs are overexpressed in many cancers and are thought to be potential drug targets (Federici et al.
; Quesada-Soriano et al.
). In plants, GSTs are often associated with herbicide resistance (Prade et al.
). In insects such as the mosquito that may be a carrier of malaria, GSTs are associated with insecticide resistance (Oakley et al.
The Seattle Structural Genomics Center for Infectious Disease (SSGCID) is a structural genomics consortium dedicated to protein structure elucidation from National Institute for Allergy and Infectious Diseases (NIAID) class A–C organisms, with an emphasis on underserved and re-emerging pathogens (Myler et al.
). One major goal is to provide a blueprint for structure-guided drug design by determining the three-dimensional structures of potential drug targets (Van Voorhis et al.
). One target organism is Coccidioides immitis
, a dust-borne pathogenic fungus that, along with the closely related species C. posadasii
, causes coccidioidomycoses (Hector & Laniado-Laborin, 2005
). C. immitis
-related coccidioidomycosis is also known as Valley Fever because the disease is highly endemic in the San Joaquin Valley in California, USA. In addition, coccidioidomycosis is endemic in semiarid regions of the southwestern United States, Mexico and parts of South America (Hector & Laniado-Laborin, 2005
). Many C. immitis
infections resolve spontaneously, although the infection is sometimes fatal, especially in immunocompromised patients or patients with disseminated and central nervous system illnesses (Deus Filho, 2009
). Existing therapies are relatively ineffective and new therapeutic options are needed (Hector & Laniado-Laborin, 2005
). The genome of C. immitis
has been sequenced (Sharpton et al.
), although many of the open reading frames have been annotated as putative uncharacterized proteins. At the start of the SSGCID project in September 2007, the Protein Data Bank (PDB) only contained structures of one C. immitis
protein: a chitinase (Bortone et al.
; Hollis et al.
Here, we report the structural characterization of one C. immitis
gene product originally annotated as a ‘putative uncharacterized protein’. This protein (UniProt accession code D2YW48; formerly Q1E7Z9) has sequence homology to ζ-class GSTs of known structure and 98% sequence identity to a C. posadasii
putative maleylacetoacetate isomerase (MAAI; UniProt entry C5PGS4; Sharpton et al.
). We determined a 2.2 Å resolution apo crystal structure of the C. immitis
D2YW48 gene product by molecular replacement using the mouse ζ-class GST (PDB entry 2cz2
; E. Mizohata, S. Morita, Y. Kinoshita, K. Nagano, H. Uda, T. Uchikubo, M. Shirouzu & S. Yokoyama, unpublished work) as a search model. In addition, we obtained a 1.85 Å resolution crystal structure of the D2YW48 gene product bound to glutathione in one half-site. In combination, the genomic sequence-similarity data, the apo structural fold and the half-site glutathione binding imply that the D2YW48 gene product is likely to be a ζ-class GST.