Introduction : Ligand-gated ion channels (LGICs) are thought to mediate a significant proportion of anesthetic effects. We built atomic level models of the glycine alpha one receptor (GlyRa1) to examine its interactions with anesthetics. We previously built models of a GlyRa1 based on a prokaryotic pentameric ion channel in the closed state from Erwinia Chrysanthemi (ELIC) (1-3). Here, we built a GlyRa1 model based on the open state structures of two new ion channels from the prokaryote Gloebacter violaceus (GLIC).(4-5) These new templates are relevant since anesthetics are thought to bind to and stabilize the open state of the GlyRa1. Methods : The 3D coordinates of two forms of GLIC (3EHZ.pdb and 3EAM.pdb) were obtained from the RCSB database. The sequence of the human GlyRa1 was obtained from the NCBI database. A BLAST sequence search was performed using the GLIC sequences. Among the best scored homologous human sequences were those of the GlyRa1. The template structures and the sequence of GlyRa1 were aligned with Discovery Studio 2.0.1 (Accelrys, San Diego, CA) and the Modeler module was used for assignment of coordinates for aligned amino acids, the construction of possible loops, and the initial refinement of amino acid sidechains. Results : The BLAST derived scores suggest a close homology between the LGICs, GLIC and ELIC. Subsequent CLUSTALW alignment of the GLIC and GlyRa1 sequences demonstrates reasonable sequence similarity. The model of the GlyRa1 is a homomer with pentameric symmetry about a central ion pore and shows significant transmembrane alpha helical and extracellular beta sheet content. Unlike our previous model based on the ELIC template, the current model based on the GLIC templates shows a continuously open pore with a partial restriction within the transmembrane region. Three of the residues notable for modulating anesthetic action are on transmembrane segments 1-3 (TM1-3) (ILE229, SER 267, ALA 288). They now line the intersubunit interface, in contrast to our previous models. However, residues from TM4 that are known to modulate a variety of anesthetic effects on this or homologous LGICs are present but could only indirectly influence an intersubunit anesthetic binding site. Normal mode analyses show an iris-like motion similar to previous results.Conclusions : A model of the GlyRa1 was constructed using homology modeling based on the GLIC templates. This model posits an intersubunit site for anesthetic binding that may communicate with the intrasubunit region of each TMD.
2009 Annual Meeting of the American Society Anesthesiologists. New Orleans. October 17 - 21 2009