Structural insights into ClpP protease side exit pore-opening by a pH drop coupled with substrate hydrolysis

Mechanism of allosteric activation in human mitochondrial ClpP protease

Human ClpP protease contributes to mitochondrial protein quality control by degrading misfolded proteins. ClpP is overexpressed in cancers such as acute myeloid leukemia (AML), where its inhibition leads to the accumulation of damaged respiratory chain subunits and cell death. Conversely, hyperactivating ClpP with small-molecule activators, such as the recently discovered ONC201, disrupts mitochondrial protein degradation and impairs respiration in cancer cells. Despite its critical role in human health, the mechanism underlying the structural and functional properties of human ClpP remains elusive. Notably, human ClpP is paradoxically activated by active-site inhibitors. All available structures of human ClpP published to date are in the inactive compact or compressed states, surprisingly even when ClpP is bound to an activator molecule such as ONC201. Here, we present structures of human mitochondrial ClpP in the active extended state, including a pair of structures where ClpP is bound to an active-site inhibitor. We demonstrate that amino acid substitutions in the handle region (A192E and E196R) recreate a conserved salt bridge found in bacterial ClpP, stabilizing the extended active state and significantly enhancing ClpP activity. We elucidate the ClpP activation mechanism, highlighting a hormetic effect where substoichiometric inhibitor binding triggers an allosteric transition that drives ClpP into its active extended state. Our findings link the conformational dynamics of ClpP to its catalytic function and provide high-resolution structures for the rational design of potent and specific ClpP inhibitors, with implications for targeting AML and other disorders with ClpP involvement.

Structural Insights into Bortezomib-Induced Activation of the Caseinolytic Chaperone-Protease System in Mycobacterium tuberculosis

The caseinolytic protease (Clp) system has recently emerged as a promising anti-tuberculosis target. The anti-cancer drug bortezomib exhibits potent anti-mycobacterial activity and binds to Mycobacterium tuberculosis (Mtb) Clp protease complexes. We determine cryo-EM structures of Mtb ClpP1P2, ClpC1P1P2 and ClpXP1P2 complexes bound to bortezomib in different conformations. Structural and biochemical data indicate that sub-stoichiometric binding by bortezomib to the protease active sites orthosterically activates the MtbClpP1P2 complex. Bortezomib activation of MtbClpP1P2 induces structural changes promoting the recruitment of the chaperone-unfoldases, MtbClpC1 or MtbClpX, facilitating holoenzyme formation. The structures of the MtbClpC1P1P2 holoenzyme indicate that MtbClpC1 motion, induced by ATP rebinding at the MtbClpC1 spiral seam, translocates the substrate. In the MtbClpXP1P2 holoenzyme structure, we identify a specialized substrate channel gating mechanism involving the MtbClpX pore-2 loop and MtbClpP2 N-terminal domains. Our results provide insights into the intricate regulation of the Mtb Clp system and suggest that bortezomib can disrupt this regulation by sub-stoichiometric binding at the Mtb Clp protease sites.

Dynamic Oligomerization Processes of Bacillus subtilis ClpP Protease Induced by ADEP1 Studied with High-Speed Atomic Force Microscopy

Bacterial ClpPs are a highly conserved family of serine proteases that associate with members of the AAA+ ATPase (ATPase associated with diverse cellular activities) family to degrade protein substrates. The antibiotic A54556 factor (ADEP1) induces uncontrolled proteolysis by forming an ATPase-independent ClpP-ADEP complex. Cryo-EM analysis of Bacillus subtilis ClpP (Bs-ClpP) has demonstrated that ADEP1 binding shifts the protease to an active extended conformation and opens its axial entry pores. However, the dynamic oligomerization processes of Bs-ClpP induced by ADEP1 remain unclear. In this study, we used a combination of biochemical studies and high-speed atomic force microscopy (HS-AFM) to reveal how ADEP1 affects the oligomerization states and protease activity of Bs-ClpP, inducing the active extended state and protease activity of Bs-ClpP. HS-AFM observations demonstrated that the Bs-ClpP tetradecamer (2R state) forms via a progression from monomers to oligomers and then from oligomers to heptamers (R state) in the presence of ADEP1. Our results suggest that ADEP1 binding to monomeric Bs-ClpP triggers conformational changes that facilitate Bs-ClpP oligomerization (R and 2R states) and activation.

Production, Purification, and Biochemical Characterization of a Novel ATP-Dependent Caseinolytic Protease from the Marine Bacterium Cobetia amphilecti KMM 296

A novel caseinolytic protease (ClpP) of the S14 family from Cobetia amphilecti KMM 296 (CamClpP), comprising 206 amino acids, with a calculated molecular weight of 22.66 kDa and a pI of 4.88, was expressed in Escherichia coli cells to verify the functional annotation of the encoding gene that has low identity with known structures. The proteolytic activity of the purified recombinant enzyme was found to be 2824 U/mg, using 1% casein as a substrate. Enzyme activity was maximal at pH 5.6 and 7.4 in phosphate buffer and was maintained over a wide pH range of 4-10. The optimum temperature for protease activity was 45 °C. The enzyme in its optimal state required the presence of either NaCl or KCl at concentrations of 0.3 and 0.2 M, respectively. The addition of the metal ions Mg2+, Ca2+, Ni2+, Mn2+, Li+, and Zn2+ at 2 mM resulted in a significant inhibition of the protease activity. However, the presence of Co2+ led to a marked activation of the enzyme in the absence of ATP. The enzyme activity was inhibited by ethanol, isopropanol, glycerol, SDS, EGTA, and EDTA. The presence of Triton X-100, acetone, DTT, and PMSF resulted in a significant increase in the CamClpP protease activity. The protease CamClpP effectively and preferentially degrades high-polymer wheat and rye flour proteins. This new proteolytic enzyme with unique properties is of great ecological and biotechnological importance.

Structure of Staphylococcus aureus ClpP Bound to the Covalent Active-Site Inhibitor Cystargolide A

The caseinolytic protease is a highly conserved serine protease, crucial to prokaryotic and eukaryotic protein homeostasis, and a promising antibacterial and anticancer drug target. Herein, we describe the potent cystargolides as the first natural β-lactone inhibitors of the proteolytic core ClpP. Based on the discovery of two clpP genes next to the cystargolide biosynthetic gene cluster in Kitasatospora cystarginea, we explored ClpP as a potential cystargolide target. We show the inhibition of Staphylococcus aureus ClpP by cystargolide A and B by different biochemical methods in vitro. Synthesis of semisynthetic derivatives and probes with improved cell penetration allowed us to confirm ClpP as a specific target in S. aureus cells and to demonstrate the anti-virulence activity of this natural product class. Crystal structures show cystargolide A covalently bound to all 14 active sites of ClpP from S. aureus, Aquifex aeolicus, and Photorhabdus laumondii, and reveal the molecular mechanism of ClpP inhibition by β-lactones, the predominant class of ClpP inhibitors.

Comparative genomics of the proteostasis network in extreme acidophiles

Extreme acidophiles thrive in harsh environments characterized by acidic pH, high concentrations of dissolved metals and high osmolarity. Most of these microorganisms are chemolithoautotrophs that obtain energy from low redox potential sources, such as the oxidation of ferrous ions. Under these conditions, the mechanisms that maintain homeostasis of proteins (proteostasis), as the main organic components of the cells, are of utmost importance. Thus, the analysis of protein chaperones is critical for understanding how these organisms deal with proteostasis under such environmental conditions. In this work, using a bioinformatics approach, we performed a comparative genomic analysis of the genes encoding classical, periplasmic and stress chaperones, and the protease systems. The analysis included 35 genomes from iron- or sulfur-oxidizing autotrophic, heterotrophic, and mixotrophic acidophilic bacteria. The results showed that classical ATP-dependent chaperones, mostly folding chaperones, are widely distributed, although they are sub-represented in some groups. Acidophilic bacteria showed redundancy of genes coding for the ATP-independent holdase chaperones RidA and Hsp20. In addition, a systematically high redundancy of genes encoding periplasmic chaperones like HtrA and YidC was also detected. In the same way, the proteolytic ATPase complexes ClpPX and Lon presented redundancy and broad distribution. The presence of genes that encoded protein variants was noticeable. In addition, genes for chaperones and protease systems were clustered within the genomes, suggesting common regulation of these activities. Finally, some genes were differentially distributed between bacteria as a function of the autotrophic or heterotrophic character of their metabolism. These results suggest that acidophiles possess an abundant and flexible proteostasis network that protects proteins in organisms living in energy-limiting and extreme environmental conditions. Therefore, our results provide a means for understanding the diversity and significance of proteostasis mechanisms in extreme acidophilic bacteria.

ECPAS/Ecm29-mediated 26S proteasome disassembly is an adaptive response to glucose starvation

The 26S proteasome comprises 20S catalytic and 19S regulatory complexes. Approximately half of the proteasomes in cells exist as free 20S complexes; however, our mechanistic understanding of what determines the ratio of 26S to 20S species remains incomplete. Here, we show that glucose starvation uncouples 26S holoenzymes into 20S and 19S subcomplexes. Subcomplex affinity purification and quantitative mass spectrometry reveal that Ecm29 proteasome adaptor and scaffold (ECPAS) mediates this structural remodeling. The loss of ECPAS abrogates 26S dissociation, reducing degradation of 20S proteasome substrates, including puromycylated polypeptides. In silico modeling suggests that ECPAS conformational changes commence the disassembly process. ECPAS is also essential for endoplasmic reticulum stress response and cell survival during glucose starvation. In vivo xenograft model analysis reveals elevated 20S proteasome levels in glucose-deprived tumors. Our results demonstrate that the 20S-19S disassembly is a mechanism adapting global proteolysis to physiological needs and countering proteotoxic stress.