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J Biol Chem, Vol. 275, Issue 2, 1201-1208, January 14, 2000
From the We have used a structure-based design strategy to
transform the polypeptide toxin charybdotoxin, which blocks several
voltage-gated and Ca2+-activated K+
channels, into a selective inhibitor. As a model system, we chose two
channels in T-lymphocytes, the voltage-gated channel Kv1.3 and the Ca2+-activated channel IKCa1. Homology
models of both channels were generated based on the crystal structure
of the bacterial channel KcsA. Initial docking of
charybdotoxin was undertaken with both models, and the accuracy of
these docking configurations was tested by mutant cycle analyses,
establishing that charybdotoxin has a similar docking configuration in
the external vestibules of IKCa1 and Kv1.3.
Comparison of the refined models revealed a unique cluster of
negatively charged residues in the turret of Kv1.3, not
present in IKCa1. To exploit this difference, three novel charybdotoxin analogs were designed by introducing negatively charged
residues in place of charybdotoxin Lys32, which lies in
close proximity to this cluster. These analogs block IKCa1
with ~20-fold higher affinity than Kv1.3. The other charybdotoxin-sensitive Kv channels, Kv1.2 and
Kv1.6, contain the negative cluster and are predictably
insensitive to the charybdotoxin position 32 analogs, whereas the
maxi-KCa channel, hSlo, lacking the cluster, is
sensitive to the analogs. This provides strong evidence for topological
similarity of the external vestibules of diverse K+
channels and demonstrates the feasibility of using structure-based strategies to design selective inhibitors for mammalian K+
channels. The availability of potent and selective inhibitors of
IKCa1 will help to elucidate the role of this channel in
T-lymphocytes during the immune response as well as in erythrocytes and
colonic epithelia.
Structure-guided Transformation of Charybdotoxin Yields an
Analog That Selectively Targets Ca2+-activated over
Voltage-gated K+ Channels*
,
,
,
,
**
Department of Physiology and Biophysics,
University of California, Irvine, California 92697, the
§ Biomolecular Research Institute, Parkville, 3052 Victoria,
Australia, ¶ Bachem Bioscience Incorporated, King of Prussia,
Pennsylvania 19406, and the
Target Discovery Department,
AstraZeneca Pharmaceuticals, Wilmington, Delaware 19850
*
This work was supported by National Institutes of Health
Grants MH59222 (to K. G. C. and M. D. C.), NS14609 (to M. D. C.), and GM54221 (to M. W. P., R. S. N., and K. G. C.); by a gift from Merck Sharp and Dohme (to K. G. C.); and by a Feodor Lynen fellowship from the Alexander von Humboldt Foundation (to H. R.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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