Ion channels are integral to many biological processes
including cell volume regulation, muscle contraction,
and the transmission of nerve impulses. We are interested
in ion channel function at the molecular level, how the
channel catalyzes the movement of ions across the cellular
membranes. Last year the first high resolution crystal
structures of a potassium channel, that of the KcsA K+
channel from Streptomyces lividans, were solved (Dyle
et al, Science (1 998) 280: 69-77). This structure represents
a large step forward towards the goal of understanding
the molecular mechanisms of K+ channels.
Although the eukaryotic K+ channels have been extensively
studied, little is known about the K+ conduction properties
of KcsA. The focus of these studies has been on examining
K+ conduction through KscA. We have adapted a planar bilayer
system for the reconstitution and high-resolution recordings
of single KcsA channels. The basic properties of this
channel were studied, including how the potassium current
varies with voltage across the bilayer. The single-channel
current-voltage relationship rectifies, with larger conductances
at negative voltages than at positive voltages.
Additionally, at positive potentials KcsA exhibits a
flickery behavior in the open state that is not observed
in negative potentials. We have also examined how the
potassium currents through KcsA for K+ over other monovalent
ions. We have found that KcsA resembles eukaryotic potassium
channels on a gross level, but it is unique in some finer
details which are being examined in greater detail.
