Structural differences of bacterial and mammalian K+ channels
Summary
Using a peptide toxin, kaliotoxin (KTX), we gained new insight into
the topology of the pore region of a voltage-gated potassium channel, mKv1.1.
In order to find new interactions between mKv1.1 and KTX we investigated
the pH-dependence of KTX block which was stronger at pHo 6.2
compared to pHo 7.4. Using site-directed mutagenesis on
the channel and the toxin we found that protonation of H34 in KTX caused
the pHo-dependence of KTX block. E350 and E353 in mKv1.1
which interact with H34 in KTX were calculated to be 4 and 7 Å away
from H34/KTX, respectively. Docking of KTX into a homology model
of mKv1.1 based on the KcsA crystal structure using this
and other known interactions as constraints showed structural differences
between mKv1.1 and KcsA within the turret (aa 348-357).
To satisfy our data we would have to modify the KcsA crystal structure
for the mKv1.1 channel orienting E350 7 Å and E353 4 Å
more towards the center of the pore compared to KcsA. This
would place E350 15 Å and E353 11 Å away from the center of
the pore instead of the distances for the equivalent KcsA residues
with 22 Å for G53 and 15 Å for G56, respectively. Bacterial
and mammalian potassium channels may have structural differences regarding
the turret of the outer pore vestibule. This topological difference
between both channel types may have substantial influence on structure-guided
development of new drugs for mammalian potassium channels by rational drug
design.
Published as:
Wrisch A, Grissmer S. 2000. Structural
differences of bacterial and mammalian K+ channels. Journal
of Biological Chemistry 275(50):39345-39353.