Probing residues in the pore-forming (M2) domain of the Cys-loop receptor homologue GLIC reveals some unusual features. (February 2015)

• Record Type: Journal Article
• Authors: Alqazzaz, Mona A.; Lummis, Sarah C. R.
• Is Part Of: Molecular membrane biology. Volume 32:Number 1(2015)
• Page Start: 26
• Page End: 31
• Publication Date: 2015-02
• Subjects: Membranes (Biology) -- Periodicals; Biochemistry -- Periodicals; Cell membranes -- Periodicals; Molecular biology -- Periodicals; 571.64
• Languages: English
• ISSNs: 0968-7688

Abstract

<abstract> <title>Abstract</title> <p>Cys-loop receptors play important roles in signal transduction. The <italic>Gloeobacter</italic> ligand-gated ion channel (GLIC) pore binds similar compounds to Cys-loop receptor pores, but has the advantage of known structures in open and closed states. GLIC is activated by protons with a <italic>p</italic>EC<sub>50</sub> of 5.4, and has a histidine residue (His 11') in its pore-forming α-helix (M2) which is involved in gating. Here we explore the role of this His and other M2 residues using two-electrode voltage clamp of mutant receptors expressed in oocytes. We show that 11'His is very sensitive to substitution; replacement with a range of amino acids ablates function. Similarly altering its location in M2 to the 8', 9', 10', 12', 13' or 14' positions ablated function. Most substitutions of Ser6' or Ile9' were also non-functional, although not Ile9'Leu and Ile9'Val. Unexpectedly, an Ile9'His substitution was constitutively active at pH 7, but closed as [H+] increased, with a <italic>p</italic>IC<sub>50</sub> of 5.8. Substitution at 2', 5' and 7' had little effect on <italic>p</italic>EC<sub>50</sub>. Overall the data show Ser6' and His11' are critical for the function of the receptor, and thus distinguish the roles of these M2 residues from those of Cys-loop receptors, where substitutions are mostly well tolerated. These data suggest modellers should be aware of these atypical features when using the GLIC pore as a model for Cys-loop receptor pores.</p> </abstract>