Analysis of differential efficacy and affinity of GABA(A) (alpha 1/alpha 2) selective modulators
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
Selective modulators of the γ-amino butyric acid (GABAA) family of receptors have the potential to treat a range of disease states related to cognition, pain, and anxiety. While the development of various α subunit-selective modulators is currently underway for the treatment of anxiety disorders, a mechanistic understanding of the correlation between their bioactivity and efficacy, based on ligand–target interactions, is currently still lacking. In order to alleviate this situation, in the current study we have analyzed, using ligand- and structure-based methods, a data set of 5440 GABAA modulators. The Spearman correlation (ρ) between binding activity and efficacy of compounds was calculated to be 0.008 and 0.31 against the α1 and α2 subunits of GABA receptor, respectively; in other words, the compounds had little diversity in structure and bioactivity, but they differed significantly in efficacy. Two compounds were selected as a case study for detailed interaction analysis due to the small difference in their structures and affinities (ΔpKi(comp1_α1 – comp2_α1) = 0.45 log units, ΔpKi(comp1_α2 – comp2_α2) = 0 log units) as compared to larger relative efficacies (ΔRE(comp1_α1 – comp2_α1) = 1.03, ΔRE(comp1_α2 – comp2_α2) = 0.21). Docking analysis suggested that His-101 is involved in a characteristic interaction of the α1 receptor with both compounds 1 and 2. Residues such as Phe-77, Thr-142, Asn-60, and Arg-144 of the γ chain of the α1γ2 complex also showed interactions with heterocyclic rings of both compounds 1 and 2, but these interactions were disturbed in the case of α2γ2 complex docking results. Binding pocket stability analysis based on molecular dynamics identified three substitutions in the loop C region of the α2 subunit, namely, G200E, I201T, and V202I, causing a reduction in the flexibility of α2 compared to α1. These amino acids in α2, as compared to α1, were also observed to decrease the vibrational and dihedral entropy and to increase the hydrogen bond content in α2 in the apo state. However, freezing of both α1 and α2 was observed in the ligand-bound state, with an increased number of internal hydrogen bonds and increased entropy. Therefore, we hypothesize that the amino acid differences in the loop C region of α2 are responsible for conformational changes in the protein structure compared to α1, as well as for the binding modes of compounds and hence their functional signaling.
Date Issued
2016-10-05
Date Acceptance
2016-10-05
Citation
Molecular Pharmaceutics, 2016, 13 (11), pp.4001-4012
ISSN
1543-8392
Publisher
American Chemical Society
Start Page
4001
End Page
4012
Journal / Book Title
Molecular Pharmaceutics
Volume
13
Issue
11
Copyright Statement
© 2016 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Molecular Pharmaceutics, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.molpharmaceut.6b00813
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000387428300039&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Life Sciences & Biomedicine
Medicine, Research & Experimental
Pharmacology & Pharmacy
Research & Experimental Medicine
benzodiazepines
GABA(A) alpha 1
GABA(A) alpha 2
relative efficacy
affinity modeling
proteochemometric modeling
selective modulators
BENZODIAZEPINE BINDING-SITE
RECEPTOR SUBTYPES
VARIABLE IMPORTANCE
RANDOM FORESTS
FORCE-FIELD
MODEL
DYNAMICS
AGONISTS
LIGANDS
PACKAGE
GABAA α1
GABAA α2
1115 Pharmacology And Pharmaceutical Sciences
Publication Status
Published