Abstract：
Targeting heterologous multi-transmembrane domain (TMD) proteins to plant chloroplasts requires sequences in addition to the chloroplast transit peptide (cTP). The N-terminal domain (N-region), located C-terminal to the cTP in chloroplast inner envelope membrane proteins, is an essential region for import. However, it was unclear if the N-region functions solely as a spacer sequence to facilitate cTP access or if it plays an active role in the import process. This study addresses the N-region\'s role by using combinations of cTPs and N-regions from Arabidopsis chloroplast inner envelope membrane proteins to direct the cyanobacterial protein SbtA to the chloroplast. We find that the sequence context of the N-region affects the chloroplast import efficiency of SbtA, with particular sequences mis-targeting the protein to different cellular sub-compartments. Additionally, specific cTP and N-region pairs exhibit varying targeting efficiencies for different heterologous proteins. Substituting individual N-region motifs did not significantly alter the chloroplast targeting efficiency of a particular cTP and N-region pair. We conclude that the N-region exhibits contextual functioning and potentially functional redundancy in motifs.
摘要：
将异源多跨膜结构域(TMD)蛋白靶向植物叶绿体需要除了叶绿体转运肽(cTP)之外的序列。N端结构域（N区），位于叶绿体内包膜蛋白中cTP的C端，是重要的进口地区。然而,目前尚不清楚N区是否仅作为间隔区序列来促进cTP的访问，或者它是否在导入过程中起积极作用。本研究通过使用拟南芥叶绿体内包膜蛋白的cTP和N区的组合将蓝细菌蛋白SbtA引导至叶绿体，从而解决了N区的作用。我们发现N区的序列上下文影响SbtA的叶绿体导入效率，特定序列错误地将蛋白质靶向不同的细胞亚区室。此外,特定的cTP和N区对对不同的异源蛋白表现出不同的靶向效率。取代单个N区基序不会显着改变特定cTP和N区对的叶绿体靶向效率。我们得出的结论是，N区在基序中表现出上下文功能和潜在的功能冗余。
