Nuclear-encoded chloroplast proteins are synthesized in the cytosol with an N-terminal transit peptide. These proteins then traverse the chloroplast envelope membranes with the help of translocon machinery in the outer and inner envelope membranes called TOC and TIC, respectively (1). Tic40 is one of the essential components of TIC machinery. Tic40 together with Hsp93 involves in protein translocation to stroma. C-terminal Np-repeat domain of Tic40 interacts with Hsp93 and stimulates ATP hydrolysis (3).
References:
1- Schleiff, E. and Becker, T. (2011) Common ground for protein translocation: access control for mitochondria and chloroplasts. Nat. Rev. Mol. Cell Biol. 12, 48-59
2- Yi-Fen Kao,Yuan-Chao Lou,Yi-Hung Yeh,Chwan-Deng Hsiao,and Chinpan Chen. (2012) Solution structure of the C-terminal NP-repeat domain of Tic40, a co-chaperone during protein import into chloroplasts. J Biochem 152(5): 443-451
3- Kovacheva, S., Bedard, J., Wardle, A., Patel, R., and Jarvis, P. (2007) Further in vivo studies on the role of the molecular chaperone, Hsp93, in plastid protein import. Plant J. 50, 364-379
