Sec‐dependent membrane protein insertion: sequential interaction of nascent FtsQ with SecY and YidC

Abstract

Recent studies identified YidC as a novel membrane factor that may play a key role in membrane insertion of inner membrane proteins (IMPs), both in conjunction with the Sec‐translocase and as a separate entity. Here, we show that the type II IMP FtsQ requires both the translocase and, to a lesser extent, YidC in vivo. Using photo‐crosslinking we demonstrate that the transmembrane (TM) domain of the nascent IMP FtsQ inserts into the membrane close to SecY and lipids, and moves to a combined YidC/lipid environment upon elongation. These data are consistent with a crucial role for YidC in the lateral transfer of TM domains from the Sec translocase into the lipid bilayer.