title: Characterization of the estradiol-binding site structure of human pancreas-specific protein disulfide isomerase: indispensable role of the hydrogen bond between His278 and the estradiol 3-hydroxyl group.
abstract: Estradiol (E(2)), a female sex hormone, has important biological functions. Human pancreas-specific protein disulfide isomerase (PDIp), a protein folding catalyst, was recently found to be able to bind E(2). Here we report the characterization of its E(2)-binding site by using biochemical methods coupled with molecular modeling tools. Analysis of various truncated PDIp proteins showed that the b-b' fragment contains an intact E(2)-binding site that has the same binding affinity as the full-length PDIp protein, with apparent K(d) values of approximately 170 nM. Computational modeling and docking analyses revealed that the E(2)-binding site in the b-b' fragment is located in a hydrophobic pocket composed mainly of the b' domain and partially of the b domain. The hydrogen bond, formed between the 3-hydroxyl group of E(2) (donor) and PDIp's His278 (acceptor), is indispensable for its binding. By contrast, the 17β-hydroxyl group of E(2) is of negligible importance for E(2) binding. This binding model was jointly confirmed by a series of experiments, such as selective mutation of the binding site amino acid residues and selective modification of the ligand structures.
authors.affiliation: Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, Kansas City, Kansas 66160, United States.
authors.forename: Xin-Miao
authors.initials: XM
authors.lastname: Fu
authors.forename: Pan
authors.initials: P
authors.lastname: Wang
authors.forename: Bao Ting
authors.initials: BT
authors.lastname: Zhu
mesh_terms: D001665:Binding Sites; D004958:Estradiol / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D062105:Molecular Docking Simulation; D010179:Pancreas / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D019704:Protein Disulfide-Isomerases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D006639:Histidine; D004958:Estradiol; D019704:Protein Disulfide-Isomerases