The γ-aminobutyric acid (GABA) A receptor is composed of a variety of subunits and combinations and shows a characteristic distribution in the CNS. To date, 20 subunits of the GABA A receptor have been cloned: α1-6, β1-4, γ1-3, δ, π, ε , Θ, and ρ1-3. Oocyte of Xenopus laevis is one of the most frequently used heterologous expression systems, which are used to design and analyze specific combinations of GABA A receptor subunits. In oocytes, a certain GABA A receptor function is studied only by comparing the amplitude of the response to GABA and other drugs by physiological and pharmacological methods. According to the studies on Xenopus laevis oocytes, the α1β2γ2S receptor combination is mostly used. The α1-containing receptors mediate sedative and anticonvulsant acts. The results of studies on oocytes show that PKA, NKCC1, P2X3 receptors, and GABA A receptor-associated protein, etc., are existing systems that show different reactivity to the GABA A receptors. The GABA A receptor subunits contain distinct binding sites for BZDs, neurosteroids, general anesthetics, etc., which are responsible for the numerous functions of the GABA A receptor. A variety of other drugs, such as topiramate, TG41, (+)- and (-)-borneol, apigenin, and 6-methylflavone could also have modulatory effects on the GABA A receptors. Some of the different models and hypotheses on GABA A receptor structure and function have been achieved by using the two-electrode voltage clamp method in oocytes.
Glioblastoma multiforme (GBM) is a high-grade brain tumor of which the survival patients remain poor.
Tousled-like kinase 1 (TLK1), a serine-threonine kinase, was identified to be overexpressed in cancers such
as GBM. TLK1 plays an important role in controlling survival pathways. To date, there is no structure
available for TLK1 as well as its inhibitors. We aimed to create a homology model of TLK1 and to identify
suitable molecular inhibitors that are likely to bind and inhibit TLK1 activity via in silico high-throughput
virtual screening (HTVS) protein-ligand docking. The 3D homology models of TLK1 were derived from
various servers. All models were evaluated using Swiss Model QMEAN server. Validation was performed
using multiple tools. Energy minimization was performed using YASARA. Subsequently, HTVS was
performed using Molegro Virtual Docker 6.0 and ligands derived from ligand.info database. Drug-like
molecules were filtered using ADME-Tox filtering program. Best homology model was obtained from the
Aurora B kinase (PDB ID:4B8M) derived from Xenopus levias structure that share sequence similarity with
human TLK1. Two compounds were identified from HTVS to be the potential inhibitors as it did not violate
the Lipinski rule of five and the CNS-based filter as a potential drug-like molecule for GBM
The α1β2γ2 subtype of GABAA receptors is the most commonly found GABAA receptor subtype in the mammalian cortex and hippocampus. It is expressed heterologously in the Xenopus laevis oocyte as a α1β2γ2S/L subtype for application as an in vitro model for the screening of compounds that modulate receptor activities. In fact, 4-hydroxybenzaldehyde (4-HB) has been identified as one of the major components in Dendrocalamus asper bamboo shoots in our previous study, and the current study showed that at 101.7 μM, 4-HB significantly reduced the GABA-induced chloride current of GABAA receptors expressed on Xenopus oocytes, indicating a possible GABAergic antagonistic effect at high concentrations.