The Structure and Function of the Chloroplast Import Apparatus

Chloroplasts, the photosynthetic organelles of plants and algae, rely on the import of thousands of nuclear-encoded proteins to sustain their diverse physiological roles. This process is mediated by the coordinated action of the translocon at the outer chloroplast membrane (TOC), the translocon at the inner chloroplast membrane (TIC), and an ATP-driven import motor. However, research on these key machineries has long been intensely debated in the field. Recent advances in structural characterization have now resolved long-standing controversies regarding the composition and architecture of these complexes. This review summarizes the most recent structural, functional, and evolutionary insights into the chloroplast protein import apparatus, emphasizing the transformative role of high-resolution structural biology in redefining long-held paradigms.