title: Molecular basis of interactions of cholinesterases with tight binding inhibitors.
abstract: Among the large variety of reversible inhibitors that bind to cholinesterases (ChE), only a few exhibit exquisitely strong binding reflected in low femtomolar to picomolar equilibrium dissociation constants. These tight binding inhibitors owe their high affinity to distinctive modes of interaction with the enzyme: naturally occurring snake toxins, the fasciculins, share a large 1000 angstroms2 complementary surface for its complex with acetylcholinesterases (AChE; EC 3.1.1.7); transition state analogs trifluoroacetophenones form a covalent bond with the active serine; disubstituted 1,2,3-triazole inhibitors formed in situ are selected by AChE for optimal interaction surface over the length of the active center gorge. All these inhibitors bind with higher affinity to AChEs than to the closely related butyrylcholinesterases (BuChE; EC 3.1.1.8). Selectivity of individual inhibitors towards BuChE increases with increasing their molecular size. Interaction kinetics for all three classes of compounds reveal very slow rates of dissociation of the AChE-inhibitor complexes or conjugates combined with very fast association rates. The influence of conformational flexibility of the active center gorge on the affinity of inhibitor binding was demonstrated by comparing binding properties of a series of disubstituted 1,2,3-triazoles having systematically varied structures. Analysis of the linear free energy relationships of binding to both mouse and Electrophorus AChE reveals independent contributions of individual structural elements of inhibitors to their binding with the triazole ring emerging as an independently contributing pharmacophore. These tight binding inhibitor interactions reveal useful information not only on the conformational flexibility of ChEs, but also on the diversity of modes of interaction that achieve inhibition.
authors.affiliation: Department of Pharmacology 0636, University of California at San Diego, La Jolla, CA 92093, USA. zradic@ucsd.edu
authors.forename: Zoran
authors.initials: Z
authors.lastname: Radić
authors.forename: Roman
authors.initials: R
authors.lastname: Manetsch
authors.forename: Antoni
authors.initials: A
authors.lastname: Krasiński
authors.forename: Jessica
authors.initials: J
authors.lastname: Raushel
authors.forename: John
authors.initials: J
authors.lastname: Yamauchi
authors.forename: Cindy
authors.initials: C
authors.lastname: Garcia
authors.forename: Hartmuth
authors.initials: H
authors.lastname: Kolb
authors.forename: K Barry
authors.initials: KB
authors.lastname: Sharpless
authors.forename: Palmer
authors.initials: P
authors.lastname: Taylor
mesh_terms: D000098:Acetophenones / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000737:chemistry* / Q000378:metabolism*; D002802:Cholinesterases / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004546:Elapid Venoms / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry
chemical_list: D000098:Acetophenones; D002800:Cholinesterase Inhibitors; D004546:Elapid Venoms; D014230:Triazoles; C044937:fasciculin; D002802:Cholinesterases; D005459:Fluorides