title: Crystal structures of an enantioselective fab-fragment in free and complex forms.
abstract: Enantioselective antibodies can separate the enantiomers of a chiral compound in a highly specific manner. We have recently reported the cloning and applications of a recombinant Fab-fragment, ENA11His, in the enantioseparation of a drug candidate, finrozole, which contains two chiral centers. Here, the crystal structures of this enantioselective antibody Fab-fragment are determined in the absence of the hapten at a resolution of 2.75 A, and in the presence of the hapten at 2.05 A resolution. The conformation of the protein was found to be similar in both free and complex forms. The hapten molecule was tightly bound in a deep cleft between the light and heavy chains of the Fab-fragment. The complex structure also allowed us to describe the molecular basis for enantioselectivity and to deduce the absolute configurations of all the four different stereoisomers (a-d) of finrozole. The ENA11His antibody fragment selectively binds the SR (a) enantiomer from the racemic mixture of a and d-enantiomers, thus allowing separation from the pharmacologically most active RS enantiomer (d). In particular, Asp95 and Asn35 of the H-chain in the ENA11 His antibody seem to provide this specificity through hydrogen bonding.
authors.affiliation: Department of Chemistry, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland.
authors.forename: Tarja
authors.initials: T
authors.lastname: Parkkinen
authors.forename: Tarja K
authors.initials: TK
authors.lastname: Nevanen
authors.forename: Anu
authors.initials: A
authors.lastname: Koivula
authors.forename: Juha
authors.initials: J
authors.lastname: Rouvinen
mesh_terms: D000818:Animals; D047072:Aromatase Inhibitors / Q000276:immunology / Q000302:isolation & purification; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006241:Haptens; D006860:Hydrogen Bonding; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D015394:Molecular Structure; D009570:Nitriles / Q000276:immunology / Q000302:isolation & purification; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D013237:Stereoisomerism; D014230:Triazoles / Q000276:immunology / Q000302:isolation & purification
chemical_list: D047072:Aromatase Inhibitors; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D009570:Nitriles; D011994:Recombinant Proteins; D014230:Triazoles; C111409:finrozole