Kohorn B D, Tobin E M
Department of Botany, Duke University, Durham, North Carolina 27706.
Plant Cell. 1989 Jan;1(1):159-66. doi: 10.1105/tpc.1.1.159.
Proteins synthesized as soluble precursors in the cytoplasm of eukaryotic cells often cross organellar membrane barriers and then insert into lipid bilayers. One such polypeptide, the light-harvesting chlorophyll a/b-binding protein (LHCP), must also associate with pigment molecules and be assembled into the photosystem II light-harvesting complex in the chloroplast thylakoid membrane. A study of the import of mutant LHCPs into isolated chloroplasts has shown that a putative alpha-helical membrane-spanning domain near the carboxy terminus (helix 3) is essential for the stable insertion of LHCP in the thylakoid. Protease digestion experiments are consistent with the carboxy terminus of the protein being in the lumen. This report also shows that helix 3, when fused to a soluble protein, can target it to the thylakoids of isolated, intact chloroplasts. Although helix 3 is required for the insertion of LHCP and mutant derivatives into the thylakoid, the full insertion of helix 3 itself requires additionally the presence of other regions of LHCP. Thus, LHCP targeting and integration into thylakoid membranes requires a complex interaction involving a number of different domains of the LHCP polypeptide.
在真核细胞细胞质中作为可溶性前体合成的蛋白质，常常跨越细胞器膜屏障，然后插入脂质双层中。一种这样的多肽，即捕光叶绿素a/b结合蛋白（LHCP），还必须与色素分子结合，并组装到叶绿体类囊体膜中的光系统II捕光复合体中。一项关于突变型LHCP导入分离叶绿体的研究表明，靠近羧基末端的一个假定的α螺旋跨膜结构域（螺旋3）对于LHCP在类囊体中的稳定插入至关重要。蛋白酶消化实验与该蛋白质的羧基末端位于腔中这一情况相符。本报告还表明，当螺旋3与一种可溶性蛋白质融合时，可将其靶向到分离的完整叶绿体的类囊体中。虽然螺旋3是LHCP及其突变衍生物插入类囊体所必需的，但螺旋3自身的完全插入还额外需要LHCP其他区域的存在。因此，LHCP靶向并整合到类囊体膜中需要涉及LHCP多肽多个不同结构域的复杂相互作用。
