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A steered molecular dynamics study of binding and translocation processes in the GABA transporter.

ABSTRACT: The entire substrate translocation pathway in the human GABA transporter (GAT-1) was explored for the endogenous substrate GABA and the anti-convulsive drug tiagabine. Following a steered molecular dynamics (SMD) approach, in which a harmonic restraining potential is applied to the ligand, dissociation and re-association of ligands were simulated revealing events leading to substrate (GABA) translocation and inhibitor (tiagabine) mechanism of action. We succeeded in turning the transporter from the outward facing occluded to the open-to-out conformation, and also to reorient the transporter to the open-to-in conformation. The simulations are validated by literature data and provide a substrate pathway fingerprint in terms of which, how, and in which sequence specific residues are interacted with. They reveal the essential functional roles of specific residues, e.g. the role of charged residues in the extracellular vestibule including two lysines (K76 (TM1) and K448 (TM10)) and a TM6-triad (D281, E283, and D287) in attracting and relocating substrates towards the secondary/interim substrate-binding site (S2). Likewise, E101 is highlighted as essential for the relocation of the substrate from the primary substrate-binding site (S1) towards the cytoplasm.

SUBMITTER: Skovstrup S

PROVIDER: S-EPMC3380839 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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A steered molecular dynamics study of binding and translocation processes in the GABA transporter.

Skovstrup Søren S David Laurent L Taboureau Olivier O Jørgensen Flemming Steen FS

PloS one 20120621 6

The entire substrate translocation pathway in the human GABA transporter (GAT-1) was explored for the endogenous substrate GABA and the anti-convulsive drug tiagabine. Following a steered molecular dynamics (SMD) approach, in which a harmonic restraining potential is applied to the ligand, dissociation and re-association of ligands were simulated revealing events leading to substrate (GABA) translocation and inhibitor (tiagabine) mechanism of action. We succeeded in turning the transporter from ...[more]

PMID: 22737235

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Project description:HIV-1 reverse transcriptase (RT) is the primary target for anti-AIDS chemotherapy. Nonnucleoside RT inhibitors (NNRTIs) are very potent and most promising anti-AIDS drugs that specifically inhibit HIV-1 RT. The binding and unbinding processes of alpha-APA, an NNRTI, have been studied using nanosecond conventional molecular dynamics and steered molecular dynamics simulations. The simulation results show that the unbinding process of alpha-APA consists of three phases based on the position of alpha-APA in relation to the entrance of the binding pocket. When alpha-APA is bound in the binding pocket, the hydrophobic interactions between HIV-1 RT and alpha-APA dominate the binding; however, the hydrophilic interactions (both direct and water-bridged hydrogen bonds) also contribute to the stabilizing forces. Whereas Tyr-181 makes significant hydrophobic interactions with alpha-APA, Tyr-188 forms a strong hydrogen bond with the acylamino group (N14) of alpha-APA. These two residues have very flexible side chains and appear to act as two "flexible clamps" discouraging alpha-APA to dissociate from the binding pocket. At the pocket entrance, two relatively inflexible residues, Val-179 and Leu-100, gauge the openness of the entrance and form the bottleneck of the inhibitor-unbinding pathway. Two special water molecules at the pocket entrance appear to play important roles in inhibitor recognition of binding and unbinding. These water molecules form water bridges between the polar groups of the inhibitor and the residues around the entrance, and between the polar groups of the inhibitor themselves. The water-bridged interactions not only induce the inhibitor to adopt an energetically favorable conformation so the inhibitor can pass through the pocket entrance, but also stabilize the binding of the inhibitor in the pocket to prevent the inhibitor's dissociation. The complementary steered molecular dynamics and conventional molecular dynamics simulation results strongly support the hypothesis that NNRTIs inhibit HIV-1 RT polymerization activity by enlarging the DNA-binding cleft and restricting the flexibility and mobility of the p66 thumb subdomain that are believed to be essential during DNA translocation and polymerization.

Dataset Information

A steered molecular dynamics study of binding and translocation processes in the GABA transporter.

Publications

A steered molecular dynamics study of binding and translocation processes in the GABA transporter.

Similar Datasets

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