ClpP2 (Rv2460c) is the proteolytic subunit of the essential ATP-dependent Clp protease in M. tuberculosis. Unlike most bacteria with a single ClpP homooligomer, Mtb requires both ClpP1 and ClpP2 to form a catalytically active heterotetradecameric complex (7 ClpP1 + 7 ClpP2 subunits). The protease uses a Ser-His-Asp catalytic triad (Ser110, His135 in ClpP2) for serine-type endopeptidase activity, with a preference for cleavage after leucine or methionine. ClpP1P2 collaborates with AAA+ unfoldases ClpC1 and ClpX, which unfold and translocate substrates into the proteolytic chamber. The complex degrades misfolded proteins for quality control and selectively degrades regulatory anti-sigma factors (RseA via ClpC1P2, RsdA via ClpP1P2-ClpX) to activate stress-responsive transcription. Both clpP1 and clpP2 are essential for Mtb viability, and ClpP1P2 is a validated drug target for tuberculosis therapy. Overexpression of clpP2 (but not clpP1) is toxic, suggesting distinct roles for the two subunits.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009368 endopeptidase Clp complex | IBA GO_REF:0000033 | ACCEPT | Summary: ClpP2 is a core subunit of the Clp protease complex. In Mtb, this is specifically the heterotetradecameric ClpP1P2 complex. The IBA annotation is well-supported by extensive structural and biochemical evidence. Reason: ClpP2 forms the ClpP1P2 heterocomplex, confirmed by crystal structure (PDB: 5DZK, 5E0S) and biochemical studies. Akopian et al. (2012) showed that only the mixed ClpP1-ClpP2 complex is proteolytically active. Supporting Evidence: PMID:22286948 reconstitute an active, mixed ClpP1P2 complex after identifying N-blocked dipeptides that stimulate dramatically (>1000-fold) ClpP1P2 activity file:MYCTU/clpP2/clpP2-deep-research-bioreason-sft.md A cytosolic protease that assembles into a tetradecameric barrel and, when engaged by AAA+ ATPase partners, degrades misfolded, damaged, or regulatory proteins |
| GO:0006515 protein quality control for misfolded or incompletely synthesized proteins | IBA GO_REF:0000033 | ACCEPT | Summary: Protein quality control is a well-established core function of Clp proteases. The ClpP1P2 complex, in collaboration with AAA+ ATPases, degrades misfolded and damaged proteins. UniProt function description states ClpP2 "plays a major role in the degradation of misfolded proteins." Reason: This is a conserved core function of ClpP proteases across bacteria. The Mtb ClpP1P2 complex specifically degrades misfolded proteins, consistent with IBA inference from E. coli ClpP (P0A6G7). Supported by biochemical evidence of processive degradation with AAA+ partners. Supporting Evidence: PMID:24976069 Mycobacterial Clp-family proteases function via collaboration of the heteromeric ClpP1P2 peptidase with a AAA+ partner, ClpX or ClpC1. These enzymes are essential for M. tuberculosis viability PMID:22123255 the proteolytic activity of ClpP in concert with the ATPase activity of the ClpX/ClpC subunits results in degradation of misfolded or damaged proteins |
| GO:0004252 serine-type endopeptidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: ClpP2 is a serine protease with a Ser-His-Asp catalytic triad. The active site serine (Ser110) acts as the nucleophile for peptide bond hydrolysis. This is a core molecular function annotation. Reason: Serine-type endopeptidase activity is confirmed by the catalytic triad (Ser110, His135), structural data, and enzymatic activity studies. ClpP1P2 prefers cleavage after leucine or methionine at the P1 position. Supporting Evidence: PMID:25759383 we show that ClpP1P2 prefers Met ≫ Leu > Phe > Ala in the X1 position PMID:22286948 ClpP1P2 possesses chymotrypsin and caspase-like activities, and ClpP1 and ClpP2 differ in cleavage preferences |
| GO:0004176 ATP-dependent peptidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: The ClpP1P2 complex carries out ATP-dependent proteolysis, but importantly the ATPase activity resides in the AAA+ partner unfoldases (ClpC1, ClpX), not in ClpP2 itself. ClpP2 contributes the peptidase activity to a complex whose overall function is ATP-dependent. The qualifier should be contributes_to rather than enables, since the ATP-dependent activity is a property of the holoenzyme complex (ClpXP1P2 or ClpC1P1P2). Reason: ClpP2 provides the proteolytic component of an ATP-dependent protease complex. ATP hydrolysis is performed by ClpX or ClpC1, not by ClpP2 itself. The annotation correctly reflects that the holoenzyme complex has ATP-dependent peptidase activity, and ClpP2 contributes to this. Supporting Evidence: PMID:24976069 Both ClpX and ClpC1 catalyse ATP-dependent unfolding and degradation of native protein substrates in conjunction with ClpP1P2 |
| GO:0051117 ATPase binding | IBA GO_REF:0000033 | ACCEPT | Summary: ClpP2 directly binds the AAA+ ATPases ClpX and ClpC1. The interaction is asymmetric: ClpX binds specifically to the ClpP2 ring, while ClpC1 can associate with either ring. This binding is essential for substrate delivery and activation of the protease. Reason: Direct binding of ClpP2 to ClpX is well-established. Leodolter et al. (2015) demonstrated that ClpX binds specifically to the ClpP2 ring. Multiple structural studies confirm the ClpP-ATPase interface. Supporting Evidence: PMID:25933022 both Mycobacterium tuberculosis Clp chaperones require the intact interaction face of ClpP2 to support degradation, resulting in an asymmetric complex where chaperones only bind to the ClpP2 side of the proteolytic core |
| GO:0004176 ATP-dependent peptidase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO annotation from IPR001907 (ATP-dependent Clp protease proteolytic subunit). Correctly captures the functional family assignment. Redundant with the IBA annotation above. Reason: Correct InterPro2GO mapping. IPR001907 is the ClpP protease family, and ATP-dependent peptidase activity is the appropriate molecular function for this family. Supported by the same biochemical evidence as the IBA annotation. |
| GO:0004252 serine-type endopeptidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA annotation from InterPro:IPR001907 and EC:3.4.21.92. Redundant with the IBA annotation but correctly assigned. Reason: Correct and well-supported annotation. EC 3.4.21.92 is the specific EC number for endopeptidase Clp, and IPR001907 maps to the ClpP family. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: Cytoplasmic localization is correct for ClpP2. The protein lacks signal peptides and transmembrane domains and functions as a soluble protease in the cytoplasm, consistent with UniProt annotation based on HAMAP-Rule MF_00444. Reason: Cytoplasmic localization is appropriate for a soluble protease subunit. No signal peptide or transmembrane domains are present. Consistent with the known biology of Clp proteases as cytoplasmic quality-control enzymes. |
| GO:0006508 proteolysis | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Proteolysis is correct but very general. The more specific annotations for protein quality control (GO:0006515) and the specific molecular function annotations provide better functional resolution. This parent term is acceptable as a broad IEA annotation. Reason: Technically correct but too general; the more informative annotations for protein quality control and specific substrate processing better describe ClpP2 function. Retained as a broad supporting annotation. |
| GO:0005515 protein binding | IPI PMID:16844784 Dissecting virulence pathways of Mycobacterium tuberculosis ... | REMOVE | Summary: This annotation derives from the M-PFC protein-protein interaction study by Singh et al. (2006). The "protein binding" term is too vague and uninformative per curation guidelines. ClpP2 has specific well-characterized protein interactions (with ClpP1, ClpX, ClpC1) that are better captured by more specific terms. The ATPase binding annotation (GO:0051117) already covers the key functional interaction. Reason: Per curation guidelines, GO:0005515 (protein binding) should be avoided as it does not convey meaningful functional information. The biologically relevant interactions of ClpP2 are captured by GO:0051117 (ATPase binding) and GO:0009368 (endopeptidase Clp complex). The IPI evidence from this high-throughput interaction screen does not add specificity. Supporting Evidence: PMID:16844784 Rv3596c (ClpC1), an AAA-ATPase chaperone involved in protein translocation and quality control |
| GO:0005886 plasma membrane | HDA PMID:14532352 Comprehensive proteomic profiling of the membrane constituen... | MARK AS OVER ANNOTATED | Summary: This annotation derives from a large-scale membrane proteomics study (Gu et al. 2003) that identified 739 proteins in the membrane fraction. The study notes that many identified proteins are soluble cytoplasmic proteins that copurify with membranes. ClpP2 lacks transmembrane domains and a signal peptide. UniProt annotates cytoplasm, not membrane. This is likely a copurification artifact rather than true membrane localization. Reason: ClpP2 is a soluble cytoplasmic protein (no TM domains, no signal peptide). The membrane proteomics study identified it as part of 739 proteins in the membrane fraction, many of which are known cytoplasmic contaminants. UniProt assigns cytoplasm via HAMAP-Rule MF_00444. The primary localization is cytoplasmic/cytosolic. Supporting Evidence: PMID:14532352 739 proteins have been identified by two or more distinct peptide sequences...approximately 450 proteins represent novel identifications, 79 of which are membrane proteins and more than 100 of which are membrane-associated proteins file:MYCTU/clpP2/clpP2-deep-research-bioreason-sft.md Although primarily soluble, it likely interfaces with membrane- and cell wall-proximal quality-control pathways during envelope stress |
Loading supporting content…
Download this section (compressed HTML)Q: What are the specific in vivo substrates of ClpP1P2 beyond the anti-sigma factors RseA and RsdA? A comprehensive substrate identification study would illuminate the full scope of ClpP1P2 regulatory functions.
Q: What is the molecular basis for the toxicity of clpP2 overexpression but not clpP1 overexpression? Does excess ClpP2 form aberrant complexes or titrate away essential partners?
Suggested experts: Ollinger J, Parish T
Q: How does the functional asymmetry between ClpP1 and ClpP2 catalytic sites affect substrate processing in vivo? Are there substrates preferentially processed by one active site over the other?
Suggested experts: Nagpal J
Experiment: Trap-and-release proteomics using catalytically inactive ClpP1P2 mutants to identify the full set of in vivo substrates in different growth conditions (exponential, stationary, stress).
Hypothesis: ClpP1P2 has a broader substrate repertoire than currently known, including regulators of virulence and persistence programs.
Experiment: Characterization of clpP2 overexpression toxicity mechanism using proteomics and genetic suppressor analysis.
Hypothesis: Excess ClpP2 may form aberrant homomeric complexes or deplete ClpP1 from functional heterocomplexes, disrupting proteostasis.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)