The machinery of membrane protein assembly.

The SecY (bacteria) and Sec61 (eukaryotes) translocon complexes, or protein-conducting channels, work in concert with bound ribosomes to insert proteins into membranes during the first step of membrane protein assembly. The crystallographic structure of an archaeal SecY translocon provides dramatic new insights into the mechanism of translocon function. This structure suggests an explanation for how the translocon can aid in establishing membrane protein topology via the positive-inside rule. The folding of membrane proteins may begin in the ribosome exit tunnel, before entering the translocon, according to cryo-electron microscopy and biophysical studies.