TIC/TOC complex

The TIC and TOC complexes are translocons located in the chloroplast of a eukaryotic cell, that is, protein complexes that facilitate the transfer of proteins in and out through the chloroplast's membrane.

This protein complex is functionally similar to the TOM/TIM Complex located on the outer and inner membranes of the mitochondria, in the sense that it too transports proteins across multiple membranes and into the lumen of an organelle.

Both complexes (TOC/TIC) are GTPases, that is, they must both hydrolyze GTP in order to power the translocation.

It is there that a signal peptidase cleaves the stromal transit peptide, only to reveal a second transit peptide sequence underneath; this time directing to the thylakoid membrane.

[4] There are at least three ways for the protein to go through the thylakoid membrane: through a ATP-hydrolyzing Type II secretion system, through a SecY translocon, or through the Tat/VSP pathway.

A diagram of a chloroplast. The TIC and TOC complexes are located on different sides of the chloroplast membrane .
Representation of Thylakoid targeting. A stromal transit peptide sequence (yellow rectangle) is exposed on the translated protein in the cytosol, which signals the ribosome and translocons to begin translocation into the stroma. Once in the stroma, signal peptidases cleave the first peptide sequence only to reveal a Thylakoid transit peptide sequence (blue rectangle). This transports the protein across the thylakoid membrane. [ 2 ]