Cleaves peptides in various proteins in a process that requires ATP hydrolysis. Has a chymotrypsin-like activity. Plays a major role in the degradation of misfolded proteins (By similarity). In the absence of CLPP3, modified ClpPR core(s) could be formed, albeit at strongly reduced levels (PubMed:23548781). Hydrolysis of proteins to small peptides in the presence of ATP and magnesium. alpha-casein is the usual test substrate. In the absence of ATP, only oligopeptides shorter than five residues are hydrolyzed (such as succinyl-Leu-Tyr-|-NHMec, and Leu-Tyr-Leu-|-Tyr-Trp, in which cleavage of the -Tyr-|-Leu- and -Tyr-|-Trp bonds also occurs). Component of the chloroplastic Clp protease core complex which consist of at least 16 proteins: CLPP4 (3 copies), CLPP5 (3 copies), CLPR4 (2 copies), ClpP1 (1 copy), CLPP6 (1 copy), CLPR2 (1 copy), CLPT1 (1 copy), CLPT2 (1 copy) and 3 copies of CLPP3 and/or CLPR1 and/or CLPR3 (PubMed:11278690, PubMed:14593120, PubMed:16766689). The core complex is organized in two heptameric rings, one containing CLPP3,4,5,6 in a 1:2:3:1 ratio and the other CLPP1 and CLPR1,2,3,4 in a 3:1:1:1:1 ratio (PubMed:21712416). Interacts with CHIP (PubMed:26085677). Mostly expressed in leaves. Also detected in stems, and to a lower extent, in roots (at protein level). Repressed in darkness. Accumulates during leaf senescence. Induced during cold acclimation (at protein level). Ubiquitinated in vitro by CHIP. Delayed embryo development and seedling lethality. Can be rescued by adding sugars to the growth medium. Belongs to the peptidase S14 family.