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[evol-psych] Rotational motion detected in gates controlling nerve impulses

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  • Ian Pitchford
    FOR IMMEDIATE RELEASE: 2 FEBRUARY 2000 (2 FEBRUARY 2000 GMT) University of Illinois at Urbana-Champaign http://www.uiuc.edu/ Rotational motion detected in
    Message 1 of 1 , Feb 2, 2000
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      University of Illinois at Urbana-Champaign

      Rotational motion detected in gates controlling nerve impulses

      CHAMPAIGN, Ill. -- Scientists who performed the first direct measurement of
      voltage-induced distance changes in ion channels -- critical components of
      the nervous system -- have reached a surprising conclusion. As reported in
      the Dec. 16 issue of Nature, the amino acids in the voltage sensor move like
      keys turning in locks, not like the simple plungers that were predicted by
      current models.

      "Within nerve cell membranes, there are special pores -- or channels -- that
      regulate the flow of sodium and potassium ions," said Paul Selvin, a
      professor of physics at the University of Illinois. "The channels open and
      close like little gates, depending on the voltage across the membrane, and
      therefore control the generation and propagation of nerve impulses."

      Because gene mutations in ion channels can cause neurological disorders, "a
      better understanding of how these channels work may aid in developing future
      treatments," said Francisco Bezanilla, the Hagiwara Professor of Neuroscience
      at the University of California at Los Angeles. "In this study, we wanted to
      find out how ion channels sense a change in voltage, and how the amino acids
      within the voltage sensors of the channels move when they open or close."

      To detect distances between specific sites in a potassium channel, graduate
      student Albert Cha at UCLA, graduate student Gregory Snyder at the U. of I.,
      Bezanilla and Selvin combined a measurement technique called luminescence
      resonance energy transfer, developed in the Selvin laboratory, with a
      molecular biology labeling technique called site-directed mutagenesis. Cha
      performed the experiments at Bezanilla's lab at UCLA.

      "We labeled particular amino acids within the ion channel, and then measured
      the change in distance as a function of voltage across the membrane,"
      Bezanilla said. "The separation increased from 26.5 angstroms when the gate
      was closed, to 29.5 angstroms when the gate was fully open."

      To determine the nature of that movement, Cha labeled other nearby sites and
      repeated their measurements. Surprisingly, some of these other amino acids
      moved apart, others moved closer together, and still others didn't appear to
      move at all.

      "These motions are not consistent with a simple translational movement, like
      that of a plunger moving up and down within the membrane," Bezanilla said.
      "But a rotational motion -- like the turning of a lock -- fits the data

      In both the open and closed states of the channel, there are charges that sit
      on the amino acids, Selvin said. The twisting of these amino acid segments
      exposes a different set of charges to the neighboring intracellular or
      extracellular fluid.

      "We think the amino acids form crevice-like invaginations in the cell
      membrane," Selvin said. "The rotational motion changes the chemical
      accessibility of the charges from the inside of the cell to the outside of
      the cell. Thus, a small conformational change can cause a significant
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