title: Structural insights into differences in drug-binding selectivity between two forms of human alpha1-acid glycoprotein genetic variants, the A and F1*S forms.
abstract: Human α(1)-acid glycoprotein (hAGP) in serum functions as a carrier of basic drugs. In most individuals, hAGP exists as a mixture of two genetic variants, the F1*S and A variants, which bind drugs with different selectivities. We prepared a mutant of the A variant, C149R, and showed that its drug-binding properties were indistinguishable from those of the wild type. In this study, we determined the crystal structures of this mutant hAGP alone and complexed with disopyramide (DSP), amitriptyline (AMT), and the nonspecific drug chlorpromazine (CPZ). The crystal structures revealed that the drug-binding pocket on the A variant is located within an eight-stranded β-barrel, similar to that found in the F1*S variant and other lipocalin family proteins. However, the binding region of the A variant is narrower than that of the F1*S variant. In the crystal structures of complexes with DSP and AMT, the two aromatic rings of each drug interact with Phe-49 and Phe-112 at the bottom of the binding pocket. Although the structure of CPZ is similar to those of DSP and AMT, its fused aromatic ring system, which is extended in length by the addition of a chlorine atom, appears to dictate an alternative mode of binding, which explains its nonselective binding to the F1*S and A variant hAGPs. Modeling experiments based on the co-crystal structures suggest that, in complexes of DSP, AMT, or CPZ with the F1*S variant, Phe-114 sterically hinders interactions with DSP and AMT, but not CPZ.
authors.affiliation: Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Nishi
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ono
authors.forename: Teruya
authors.initials: T
authors.lastname: Nakamura
authors.forename: Naoko
authors.initials: N
authors.lastname: Fukunaga
authors.forename: Miyoko
authors.initials: M
authors.lastname: Izumi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Ayaka
authors.initials: A
authors.lastname: Suenaga
authors.forename: Toru
authors.initials: T
authors.lastname: Maruyama
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Yamagata
authors.forename: Stephen
authors.initials: S
authors.lastname: Curry
authors.forename: Masaki
authors.initials: M
authors.lastname: Otagiri
mesh_terms: D000639:Amitriptyline / Q000737:chemistry; D002746:Chlorpromazine / Q000494:pharmacology; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods; D004206:Disopyramide / Q000737:chemistry; D014644:Genetic Variation; D006801:Humans; D054834:Lipocalins / Q000737:chemistry; D008954:Models, Biological; D009154:Mutation; D009961:Orosomucoid / Q000737:chemistry* / Q000235:genetics*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D054834:Lipocalins; D009961:Orosomucoid; D000639:Amitriptyline; D004206:Disopyramide; D002746:Chlorpromazine