The <scp>C</scp>‐terminal regions of <scp>YidC</scp> from <i><scp>R</scp>hodopirellula baltica</i> and <i><scp>O</scp>ceanicaulis alexandrii</i> bind to ribosomes and partially substitute for <scp>SRP</scp> receptor function in <i><scp>E</scp>scherichia coli</i>

Abstract

The marine Gram-negative bacteria Rhodopirellula baltica and Oceanicaulis alexandrii have, in contrast to Escherichia coli, membrane insertases with extended positively charged C-terminal regions similar to the YidC homologues in mitochondria and Gram-positive bacteria. We have found that chimeric forms of E. coli YidC fused to the C-terminal YidC regions from the marine bacteria mediate binding of YidC to ribosomes and therefore may have a functional role for targeting a nascent protein to the membrane. Here, we show in E. coli that an extended C-terminal region of YidC can compensate for a loss of SRP-receptor function in vivo. Furthermore, the enhanced affinity of the ribosome to the chimeric YidC allows the isolation of a ribosome nascent chain complex together with the C-terminally elongated YidC chimera. This complex was visualized at 8.6 Å by cryo-electron microscopy and shows a close contact of the ribosome and a YidC monomer.