Molecular Dynamic Simulations of Gabaergic Ciclic Ketones: Interaction with membranes and their contrast with experimental results

MIGUEL V; SANCHEZ-BORZONE M; GARCÍA DA

Jornada; Jornada Vincular para crecer. Camino hacia los 20 años del ICTA; 2015

The GABAA receptor (GABA-R) is the main inhibitory receptor of the Central Nervous System. It possesses  binding  sites  for  drugs  other  than  the  neurotransmitter  GABA,  including benzodiazepines,  barbiturates,  and  the  convulsing  picrotoxine,  which  behave  as  allosteric modulators or channel blockers. The study of this last binding site is especially relevant since it constitutes  the  target  of  widely  used  neurotoxic  organochlorine  pesticides  with  agricultural importance.  Our  group  has  studied  some  highly  lipophilic  cyclic  ketones  demonstrating  their ability  to  inhibit  the  GABA-R  activity.  Many  lipophilic  compounds  that  regulate  GABAA-R function may change the physical properties of the lipid bilayer. In the present work, we show Molecular Dynamics (MD) Simulation studies of the interaction of cyclic ketones with gabaergic activity,  using  a  model  bilayer  of  1,2-dipalmitoyl-sn-glycero-3-phosphocholine  (dpPC).  Free diffusion MD simulations of dpPC in presence of the different ketones were used to analyze their interaction with a bilayer. These studies revealed a looser packing in the hydrocarbon chains of the dpPC in presence of these ketones. Additionally, we obtained spatially resolved free energy profiles  of  ketones  partition  into  dpPC  bilayers  based  on  umbrella  sampling.  These  profiles allowed  us  to  determine  the  most  probable  ketones-dpPC  interaction  site.  MD  simulations results  were  contrasted  with  experimental  data  and  agreements  were  found.  Fluorescence anisotropy studies with different probes (DPH and TMA-DPH) indicated that all compounds were able to increase the membrane fluidity in a concentration dependent manner, and their effects were evidenced at different depth of the bilayer. Considering that the functions of proteins in the membrane might be altered as a result of the bilayer properties like elasticity, fluidity, thinning, etc.,  it  is  expected  that  GABAA-R  could  be  also  modulated  not  only  by  the  specific  ligand recognition, but also by changes in the physical state of the membrane.