前体蛋白与叶绿体外表面结合

1、structure and function ofstructure and function ofprotein transport protein transport machineries in chloroplastsmachineries in chloroplasts 左冰峰 杨洋 06/11/7chloroplastschloroplaststhe chloroplasts is an ognanelle chloroplasts is an ognanelle of prokaryotic of prokaryotic origin that is origin that is

2、 situated in an eukaryotic cellular situated in an eukaryotic cellular environmentenvironment .chloroplastschloroplastssix subcompartments : an inner envelope membrane an outer envelope membrane intermembrane space stroma thylakiod membrane thylakiod lumen protein transport mechanisms the two stypes

3、 : import of nuclear-encoded proteins into the chloroplast stroma through envelope membrane protein transport into thylakiod lumen across the thylakoid membraneimport of proteins into the chloroplast stroma process: .前体蛋白与叶绿体外表面结合: 前体蛋白n端的转运肽转运肽(transit peptides)和叶绿体外表面蛋白转运复合体上受体的相互作用;需少量atp. .转运的早期

4、阶段:在gtp或低浓度的atp存在下,前体蛋白与蛋白转运复合体蛋白转运复合体(translocation complexes)紧密结合. .转运末期:前体蛋白穿膜转运进入叶绿体基质,在分子伴侣分子伴侣(cytosolic chaperone)的协助下加工成为成熟的蛋白.transit peptides (转运肽)general features : a high content inhydroxylated residues; an almost completelack of acidic residues ; an overall hydrophilicnature. a number o

5、f transit peptides phosphorylationin the cytosol could support their associationwith guidance complexes.transit peptides (转运肽) structure:transit peptide contains three parts:n端含非极性氨基酸残基参与前体蛋白与受体的结合。中间段富含羟基和带正电荷的氨基酸残基参与前体蛋白的精确定位。c端形成双极性的折叠 与转运后转运肽准确切割有关。transit peptides (转运肽)the general founction: ta

6、rget the protein to chloroplast it provides an “address”that locatizes the polypeptide to one of the subcompartments.after reaching the organelle stroma, they are removed by a stromal processing peptidase(spp)cytosolic chaperone 14-3-3 proteins and hsp70在蛋白转运前,对前体蛋白进行解折叠,使其从杂的空间结构变成线型结构,以便于进行穿膜输;进入叶

7、绿体的蛋白质,又在监护蛋白的作用下重新恢复其空间构象并实施其功能.translocation complexes they are oligomeric protein complexes .they are divided into toc complex and tic complex.it is initiated by energy-independent binding of the precursor protein to surface exposed receptors followed by gtp- andatp dependent partialtranslocation

8、 across the outer envelope membrane. translocation complexes toc complexs: the toc complex which was first isolatedfrom pea chloroplasts consists of threeproteins that are designated according totheir molecular weight as toc34, toc75,and toc159 .import of proteins into the chloroplast stromatoc34 an

9、d toc159 are receptor proteins thatare responsible for the initial binding of theprecursor proteins, binding and hydrolysis ofgtp, showing highest affinity for precursors inthe gtp-form . toc159 is embedded within the outerenvelope with a cooh-terminal membraneanchor domain (m-domain), while both th

10、enh2-terminal acidic domain (a-domain) andthe centralgtp binding domain (g-domain)are exposed to the cytosol. import of proteins into the chloroplast stromatoc34 is likewise embedded within the membranewith a cooh-terminal anchor. remarkably, itshydrophilic cytosolic domain shows significanthomology

11、 to the g-domain of toc159 extendingbeyond the g-motifs conserved in all gtp-bindingproteins .toc34 is the initial receptor that transfers theprecursor protein to toc159 by a heterodimerizationstep. toc159 was furthermore shown to operate asgtp-driven motor in the translocation process import of proteins into the chloroplast stroma toc75 is a polytopic membrane protein with presumably 16 amphiphilic b-sheets which form a cation-selective ion channel within the membrane. toc75 interacts with both toc34 and toc159 and possesses a lowaffinity precursor binding site which st