FIGURE 3.

Roles of CHIP in chloroplast protein quality control (PQC). A majority of chloroplast proteins are nuclear-encoded and synthesized as precursor proteins (pre-proteins) in the cytosol. Import of these precursors proteins into chloroplasts is through the joint action of molecular machines named translocon at the outer envelope membrane (OM) of chloroplast (TOC), and translocon at the inner envelope membrane (OIM) of chloroplast (TIC). CHIP targets the degradation of misfolded and accumulated chloroplast precursor proteins such as light-harvesting complex (LHC) and Rubisco small (RbcS) subunits, which can aggregate and interfere with the chloroplast protein import. CHIP can also target the degradation of accumulated and misfolded ClpP and filamentation temperature sensitive H (FtsH) protease subunit pre-proteins to help maintain the balance among different subunits for assembly into active protease complexes. ClpP and FtsH target the degradation of misfolded, physiologically, and stress-damaged proteins insides the chloroplasts.