A negative charge in the M2 transmembrane segment of the neuronal α7 acetylcholine receptor increases permeability to divalent cations

FEBS Letters

Montal, Mauricio¹  Ferrer-Montiel, Antonio V.¹ 

[1] Department of Biology, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0319, USA

关键词: Channel protein;    Ionic selectivity;    Ionic pore;    α-Helix;    Signal transduction;    AChRα7wt;    wild type α7 acetylcholine receptor;    AChRα7D244;    site-specific mutant of AChRα7;    Px /P Na;    relative permeability of ion X with respect to Na+;    ACh;    acetylcholine;    V r reversal potential;    I;    ionic current;    NMG;    N-methyl-d-glucamine;    GHK;    Goldman-Hodgkin-Katz relative permeability equation;    the single-letter amino acid code is used;   

DOI  :  10.1016/0014-5793(93)81390-L

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Threonine-244 (T244) in the putative channel-forming M2 segment of the neuronal α7 acetylcholine receptor (AChR), a residue proposed to form part of the selectivity filter, was mutated to aspartic acid to examine the influence of a negative charge on AChR ion permeation properties. Wild type (AChRα7wt) and mutant (AChRα7D244) acetylcholine receptors expressed in Xenopus oocytes give rise to acetylcholine (ACh)-activated, α-bungarotoxin-sensitive, cation-selective ionic currents. AChRα7D244 exhibited larger currents than AChRα7wt that, in addition, activated at lower ACh concentrations. The relative ionic permeability (P _x/P _Na) of AChRα7wt to K⁺ was P _K/P _Na = 1.2, and to Ba²⁺, P _Ba/P _Na = 1.4. In contrast, AChR α7D244 was less selective in discriminating between K⁺ and Na⁺, P _k/P _Na = 0.95, but exhibited a remarkable increase in permeability to Ba²⁺, P _Ba/P _Na = 3.7. Furthermore, only mutant receptors were permeable to Mg²⁺. Hence, a ring of negatively charged residues in the putative pore-forming segment of the receptor increases the permeability to divalent cations. Our results substantiate the notion that T244, or its equivalent, in the M2 transmembrane segment of cholinergic receptor channels is a key structural determinant of the selectivity filter.

【 授权许可】

Unknown