A basic cluster determines topology of the cytoplasmic M3-M4 loop of the glycine receptor alpha1 subunit.
The inhibitory glycine receptor is a member of the ligand-gated ion channel superfamily of neurotransmitter receptors, which are composed of homologous subunits with four transmembrane segments (M1-M4), each. Here, we demonstrate that the correct topology of the glycine receptor alpha1 subunit depends critically on six positively charged residues within a basic cluster, RFRRKRR, located in the large cytoplasmic loop (designated M3-M4 loop) following the C-terminal end of M3. Neutralization of one or more charges of this cluster, but not of other charged residues in the M3-M4 loop, led to an aberrant translocation into the endoplasmic reticulum lumen of the M3-M4 loop. However, when two of the three basic charges located in the ectodomain linking M2 and M3 were neutralized, in addition to two charges of the basic cluster, endoplasmic reticulum disposition of the M3-M4 loop was prevented. We conclude that a high density of basic residues C-terminal to M3 is required to compensate for the presence of positively charged residues in the M2-M3 ectodomain, which otherwise impair correct membrane integration of the M3 segment.
Sadtler
Sven
S
Department of Molecular Pharmacology, Medical School of the Technical University of Aachen, Wendlingweg 2, D-52074 Aachen, Germany.
Laube
Bodo
B
Lashub
Alhassan
A
Nicke
Annette
A
Betz
Heinrich
H
Schmalzing
Günther
G
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D018009:Receptors, Glycine / Q000737:chemistry* / Q000235:genetics*; D013329:Structure-Activity Relationship; D014981:Xenopus
D018009:Receptors, Glycine