structure and function of protein transport ….pptVIP

Import of proteins into the chloroplast stroma Tic complex Tic22 was identified as a soluble protein that is assumed to be the first Tic component interacting with the incoming precursor protein. Tic20 is integral membrane protein presumably involved in the formation of the protein translocation pore. Import of proteins into the chloroplast stroma Tic110 is shown to form a cation selective channel(阳离子选择通道).Moreover it contains a large hydrophilic（亲水的） domain which extends into the stroma where it might provide the docking site for precursor proteins and molecular chaperones（分子伴侣）. Tic55, Tic32, and Tic62, on the other hand, might be involved in the proposed redox regulation of chloroplast protein import . protein transport into thylakoid lumen ☆protein destined for the thylakoid should contain both a stroma-targeting domain(基质靶结构域) and a thylakiod-transfer domain(类囊体转移结构域) at their N-terminus, which is removed by thylakoidal processing peptidase(TPP) after enter into the lumen. ☆many of the proteins which are encoded by chloroplast genes and synthesized on the membrane-bound ribosome are reside within thylakoid membrane. protein transport into thylakoid lumen Distinct pathways: ★Sec-dependent pathway ★SRP-dependent pathway ★ ⊿pH/Tat-dependent pathway ★ ‘spontaneous’ pathway Tat:twin arginine translocation protein transport into thylakoid lumen The SRP-dependent pathway is energized by hydrolysis of GTP and by the transthylakoidal proton gradient in an as yet unknown manner. The SRP-dependent transport is exclusively targeting integral membrane proteins and are specific for the insertion of proteins into the thylakoid membrane . protein transport into thylakoid lumen SRP-dependent transport provides the major pathway for the integration of polytopic thylakoid membrane proteins. The main representative of this class of thylakoid proteins —— LHCP which is the apoprotein(脱辅基蛋白） of the light harvesting complex associated with photosystem II. prot