POTASSIUM-DEPENDENT MOLECULES 213
N - terminal end. The researchers also found that inactivation peptides are
effective when attached to the N - terminal ends of either the α or β subunits
of the T1 4 β 4 complex apparently because these sites are close to each other in
the complex. Through several experiments co - expressing elements of the dif-
ferent T1 4 β 4 complexes the authors determined that the T1 domain does not
participate directly in activation but serves to hold theβ subunit in place.
Single - site amino acid alterations were carried out to show that mutations
in the T1 domain loop region disrupt β subunit binding to the α subunit and
abolish inactivation. Similar mutations on the β subunit surface that contacts
the T1 domain also affected inactivation. The conclusion is that both subunits
are necessary for inactivation peptides to carry out their function.
The aqueous channel down the center of the T1 4 β 4 complex is narrow ( ∼ 4 Å )
and positively charged. This channel could not allow passage of the large TEA
ion or an inactivation peptide. So how do these species navigate through the
T1 4 β 4 complex to reach the ion conduction pore? Or “ How does the ion
pathway connect to the cytoplasm? ” in the words of the reference 16 authors.
Figure 5.6 Composite model of a voltage - dependent K + channel. (From Figure 5 of
reference 16. Reprinted with permission of AAAS.) (See color plate)
S1-
S4S1-
S4NH 2*
**
*ConnectorsT1 domainβ subunit