title: An antibody exo Diels-Alderase inhibitor complex at 1.95 angstrom resolution.
abstract: A highly specific Diels-Alder protein catalyst was made by manipulating the antibody repertoire of the immune system. The catalytic antibody 13G5 catalyzes a disfavored exo Diels-Alder transformation in a reaction for which there is no natural enzyme counterpart and that yields a single regioisomer in high enantiomeric excess. The crystal structure of the antibody Fab in complex with a ferrocenyl inhibitor containing the essential haptenic core that elicited 13G5 was determined at 1.95 angstrom resolution. Three key antibody residues appear to be responsible for the observed catalysis and product control. Tyrosine-L36 acts as a Lewis acid activating the dienophile for nucleophilic attack, and asparagine-L91 and aspartic acid-H50 form hydrogen bonds to the carboxylate side chain that substitutes for the carbamate diene substrate. This hydrogen-bonding scheme leads to rate acceleration and also pronounced stereoselectivity. Docking experiments with the four possible ortho transition states of the reaction explain the specific exo effect and suggest that the (3R,4R)-exo stereoisomer is the preferred product.
authors.affiliation: The Skaggs Institute of Chemical Biology, Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: A
authors.initials: A
authors.lastname: Heine
authors.forename: E A
authors.initials: EA
authors.lastname: Stura
authors.forename: J T
authors.initials: JT
authors.lastname: Yli-Kauhaluoma
authors.forename: C
authors.initials: C
authors.lastname: Gao
authors.forename: Q
authors.initials: Q
authors.lastname: Deng
authors.forename: B R
authors.initials: BR
authors.lastname: Beno
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.forename: K D
authors.initials: KD
authors.lastname: Janda
authors.forename: I A
authors.initials: IA
authors.lastname: Wilson
mesh_terms: D017151:Antibodies, Catalytic / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D002384:Catalysis; D002625:Chemistry, Organic; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D006241:Haptens / Q000737:chemistry / Q000276:immunology; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry; D000075163:Metallocenes; D008958:Models, Molecular; D055601:Organic Chemistry Phenomena; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: C111222:1-carboxy-1'-((dimethylamino)carbonyl)ferrocene; D017151:Antibodies, Catalytic; D005296:Ferrous Compounds; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D000075163:Metallocenes