Second and Third Transmembrane Domains of the Alpha-1 Subunit of Human Glycine Receptor
[GLRA1_HUMAN] Defects in GLRA1 are the cause of hyperekplexia, hereditary, type 1 (HKPX1) [MIM:149400]. A neurologic disorder characterized by muscular rigidity of central nervous system origin, particularly in the neonatal period, and by an exaggerated startle response to unexpected acoustic or tactile stimuli. [:]        
[GLRA1_HUMAN] The glycine receptor is a neurotransmitter-gated ion channel. Binding of glycine to its receptor increases the chloride conductance and thus produces hyperpolarization (inhibition of neuronal firing).
Publication Abstract from PubMed
A 61-residue polypeptide resembling the second and third transmembrane domains (TM23) of the alpha-1 subunit of human glycine receptor and its truncated form, both with the wild-type loop linking the two TM domains (the "23" loop), were studied using high-resolution NMR. Well-defined domain structures can be identified for the TM2, 23 loop, and TM3 regions. Contrary to the popular model of a long and straight alpha-helical structure for the pore-lining TM2 domain for the Cys-loop receptor family, the last three residues of the TM2 domain and the first eight residues of the 23 loop (S16-S26) seem to be intrinsically nonhelical and highly flexible even in trifluoroethanol, a solvent known to promote and stabilize alpha-helical structures. The six remaining residues of the 23 loop and most of the TM3 domain exhibit helical structures with a kinked pi-helix (or a pi-turn) from W34 to C38 and a kink angle of 159 +/- 3 degrees . The tertiary fold of TM3 relative to TM2 is defined by several unambiguously identified long-range NOE cross-peaks within the loop region and between TM2 and TM3 domains. The 20 lowest-energy structures show a left-handed tilt of TM3 relative to TM2 with a tilting angle of 44 +/- 2 degrees between TM2 (V1-Q14) and TM3 (L39-E48) helix axes. This left-handed TM2-TM3 arrangement ensures a neatly packed right-handed quaternary structure of five subunits to form an ion-conducting pore. This is the first time that two TM domains of the glycine receptor linked by the important 23 loop have ever been analyzed at atomistic resolution. Many structural characteristics of the receptor can be inferred from the structural and dynamical features identified in this study.
Structure and dynamics of the second and third transmembrane domains of human glycine receptor.,Ma D, Liu Z, Li L, Tang P, Xu Y Biochemistry. 2005 Jun 21;44(24):8790-800. PMID:15952785
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.