Condensed Matter Physics Seminar
Thursday, May 11, 2000, 2 p.m.
Plant Sciences Building, Room 1130
Gating of membrane channels by voltage and stretch
Marco Colombini and Sergei Sukharev
(Department of Biology, University of Maryland)
Abstract: The goal of this seminar is to present two ongoing
biophysical projects to physicists on this campus. We describe two proteins
that form water-filled pores called channels in lipid membranes. Their
general function is the establishment of specific types of communication
between membrane-separated compartments in the cell. One channel
(called VDAC) is a protein found in mitochondrial membranes. Voltages
in the 10 to 30 mV range induce reversible structural changes resulting
in drastic changes in pore diameter and ion selectivity. This voltage-gating
can be amplified or diminished. Evidence will be presented for the
molecular basis for ion selectivity, voltage-sensing, and the structural
changes responsible for the changes in function. Another channel,
the Large-conductance mechanosensitive channel (called MscL), opens a 3
nm pore when the tension in the membrane reaches approximately 10
dynes/cm. Kinetic analysis of gating transitions predicts the presence
of elastic elements in the channel structure. Based on the crystal structure
of the closed conformation of the protein, we propose the sequence of molecular
events that leads to the channel opening. Questions of general physical
interest pertaining to these systems will be discussed.
Host: Victor Yakovenko
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