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Magleby/Elsevier
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# V& d6 M, R+ R* q* _, {6 z0 J& UThe gating mechanism of a K channel includes a perfect spring, according to Xiaowei Niu, Xiang Qian, and Karl Magleby (University of Miami, Miami, FL).& ^4 @4 c5 E4 f% E: t6 m8 Q/ q
) p2 n, T4 ?/ ~' j3 }+ l/ R( |The group studied the BK channel from mice. This channel is opened by changes in both voltage and intracellular Ca2 concentration. Depolarization drives a positively charged section of the protein outwards and thus drags apart the S6 channel domains that form the channel's gate. Addition of Ca2 , by contrast, widens the diameter of an intracellular gating ring, once again pulling apart the S6 gates.
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* ?, Q: ^, N" iThe two control mechanisms converge on the same target〞positioning of the S6 gates〞so one control mechanism can be used to probe the mechanism used by the other. The authors changed the length of the linkers that run from gating ring to gates, and tested how much voltage was needed to open the new channel variants.# M% p4 n/ z L; |3 W
, [+ F0 M/ l" \! R5 [) Z5 u8 JShortening the linkers made it easier to open the channel with voltage changes, probably because the diameter of the gating ring is fixed, so shortening the linker pulls the S6 gates outwards toward the gating ring. Lengthening the linker made it more difficult to open the channel with a voltage change. There was a linear relationship between the changes in linker length and required voltage, indicating that the linker-gating ring complex is acting as a perfect, Hookean spring.! J: h+ x- B8 c) y
. {' ] I' x4 sThe same linear relationship did not hold up when channels with different linker lengths were probed with varying Ca2 levels. "With calcium the gating ring becomes an active machine and changes in shape," says Magleby.
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8 Q( V; W: g9 w+ Q YMagleby hopes to confirm the proposed movements with fluorescence proximity probes. But already, says Niu, "you don't have to look at the channels as blobs of protein. You can have mechanical models that really work."/ W: q8 v; c" T3 o$ K8 P
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Niu, X., et al. 2004. Neuron. 42:745–756.(The linker between the RCK gating ring a) |
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发表于 2009-3-6 08:11
发表于 2015-6-10 09:27
