="an ">&ensp;</span>protein <span  title="" class="an ">&ensp;</span>extrinsic <span  title="" class="an ">&ensp;</span>to <span  title="" class="an ">&ensp;</span>the <span  title="" class="an ">&ensp;</span>pore <span  title="" class="an ">&ensp;</span>domain <span  title="" class="an ">&ensp;</span>is <span  title="" class="an ">&ensp;</span>necessary <span  title="" class="an ">&ensp;</span>and <span  title="" class="an ">&ensp;</span>sufficient <span  title="" class="an ">&ensp;</span>to <span  title="