The divalent cation-binding sites of gramicidin A transmembrane ion-channel.
The conductance of the gramicidin A single channels in glycerolmonooleate membranes is strongly reduced in the presence of Mn2+ cations. The nmr experiments were performed for N-terminal to N-terminal gramicidin A dimer formed by two right-handed single-stranded helixes incorporated into the sodium dodecyl sulfate micelles in the presence of Mn2+ ions. Dependence of the nonselective spin-lattice relaxation rates of the gramicidin A protons on Mn2+ concentration was analyzed to determine coordinates of the divalent cation binding sites. It is inferred that Mn2+ ions are bound at the channel mouths at distances of 6.4, 8.6, and 8.8 A (+/- 2 A) from the oxygen atoms of exposed carbonyl groups of D-Leu 12, 14, and 10, respectively. The bounded Mn2+ retains its hydrate shell, the size of which (approximately 6 A) exceeds the inner pore diameter (approximately 4 A). That makes the gramicidin A channel impermeable for divalent cations.
Golovanov
A P
AP
Shemyakin Institute of Bioorganic Chemistry, USSR Academy of Sciences, Moscow.
Barsukov
I L
IL
Arseniev
A S
AS
Bystrov
V F
VF
Sukhanov
S V
SV
Barsukov
L I
LI
D001665:Binding Sites; D002412:Cations; D004563:Electrochemistry; D006096:Gramicidin / Q000737:chemistry / Q000378:metabolism*; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D008958:Models, Molecular
D002412:Cations; D007473:Ion Channels; D006096:Gramicidin; D008345:Manganese