摘要Thousands of nuclear-encoded proteins are transported into chloroplasts through the TOC-TIC translocon that spans the chloroplast envelope membranes.A motor complex pulls the translocated proteins out of the TOC-TIC complex into the chloroplast stroma by hydrolyzing ATP.The Orf2971-FtsHi complex has been suggested to serve as the ATP-hydrolyzing motor in Chlamydomonas reinhardtii,but little is known about its architecture and assembly.Here,we report the 3.2-? resolution structure of the Chlamydomonas Orf2971-FtsHi complex.The 20-subunit complex spans the chloroplast inner envelope,with two bulky modules protruding into the intermembrane space and stromal matrix.Six subunits form a hetero-hexamer that potentially provides the pulling force through ATP hydrolysis.The remaining subunits,including potential enzymes/chaperones,likely facilitate the complex assembly and regulate its proper function.Taken together,our results provide the structural foundation for a mechanistic understanding of chloroplast protein translocation.