9.B.166 The Chloroplastic Cold-regulated 413 inner membrane protein 1, Cor413im1 (Cor413im1) Family

The inner envelope membrane (IEM) of the chloroplast plays crucial roles in forming an osmotic barrier and controlling metabolite exchange between the organelle and the cytosol. The IEM therefore harbours a number of membrane proteins and requires the import and integration of these nuclear-encoded proteins for its biogenesis. The transmembrane segment of single-spanning IEM proteins plays key roles in determining their IEM localization. Okawa et al. 2014 investigated the targeting mechanism of the polytopic IEM protein Cor413im1 which does not utilize a soluble intermediate for its targeting to the IEM. The fifth putative TMS of Cor413im1 is necessary for its targeting to the IEM, but the fifth transmembrane segment alone is insufficient to target a fusion protein to the IEM. Thus, the targeting of polytopic membrane proteins to the chloroplast IEM in vivo involves multiple transmembrane segments; chloroplasts have apparently evolved a unique mechanism for the integration of polytopic proteins to the IEM.