TLL1 (tolloid-like protein 1, mammalian tolloid-like 1) is a secreted astacin-family (peptidase M12A) zinc metalloproteinase of the BMP1/tolloid group. It is made as a precursor with a signal peptide and an N-terminal prodomain that is removed by furin-type proprotein convertases, followed by the catalytic astacin domain (HEXXH zinc-binding motif) and a non-catalytic array of five CUB and two calcium-binding EGF-like domains. Outside the cell, TLL1 cleaves a set of extracellular precursors: it removes the C-propeptides of fibrillar procollagens I and II (procollagen C-proteinase activity, enhanced by PCOLCE1, which TLL1 binds), processes procollagen VII, pro-lysyl oxidase and probiglycan, cleaves the BMP antagonist chordin, activates latent myostatin by cleaving its propeptide, and cleaves the axon-guidance cue SLIT2. Full-length TLL1 forms calcium-dependent dimers that restrain its activity relative to BMP1. TLL1 acts partly redundantly with BMP1 in collagen and matrix maturation. Loss of Tll1 in mice causes mid-gestation death with defects of the interventricular septum and heart position, and combined postnatal loss of Tll1 and Bmp1 produces brittle bones. In humans, heterozygous TLL1 variants are associated with atrial septal defect 6, and a gain-of-function variant segregates with mitral valve prolapse.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001501 skeletal system development | TAS PMID:8661043 Characterization of a novel gene product (mammalian tolloid-... | KEEP AS NON CORE | Summary: TAS annotation citing the original cloning paper for mouse mTll. That paper reports the sequence, domain structure, expression overlap with BMP-1/mTld and brain expression; it does not present skeletal data. Reason: The cited paper (abstract only in cache) is a cloning and expression study and does not by itself support a skeletal role. Independent support exists: TLL1 is an in vivo procollagen C-proteinase (PMID:12808086), and induced postnatal ablation of both Bmp1 and Tll1 in mouse produces an osteogenesis imperfecta-like phenotype with reduced procollagen processing (PMID:24419319). TLL1 therefore does part of the work of skeletal matrix formation by processing procollagen, but the in vivo skeletal evidence is from a combined two-gene knockout in mouse and is pleiotropic. Kept as a non-core developmental process. Supporting Evidence: PMID:24419319 Bones of the conditionally null mice are dramatically weakened and brittle, with spontaneous fractures-defining features of OI. PMID:24419319 reduced processing of procollagen and dentin matrix protein 1 |
| GO:0004222 metalloendopeptidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic propagation of metalloendopeptidase activity from the deep astacin node PTN000013301 in PTHR24251. Reason: Correct and core. TLL1 is an astacin (M12A) zinc metalloproteinase with the conserved zinc-binding active site, and recombinant human TLL1 has measured endopeptidase activity against chordin and procollagen I (PMID:30538173) and against SLIT2 (PMID:41626796). The IBA node placement is consistent with the experimental data on the gene itself. Supporting Evidence: PMID:30538173 Corresponding recombinant proteins were analyzed for their metalloendopeptidase activity using a native substrate, chordin. file:human/TLL1/TLL1-uniprot.txt FT ACT_SITE 241 |
| GO:0004222 metalloendopeptidase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the peptidase M12A and BMP1/tolloid-like signatures. Reason: The domain mapping agrees with direct biochemical evidence for the human enzyme (PMID:30538173, PMID:10479448). Supporting Evidence: file:human/TLL1/TLL1-uniprot.txt DR InterPro; IPR001506; Peptidase_M12A. PMID:10479448 mTLL-1 is shown to specifically process procollagen C-propeptides at the physiologically relevant site |
| GO:0004222 metalloendopeptidase activity | TAS Reactome:R-HSA-2002440 | ACCEPT | Summary: Reactome reaction for removal of fibrillar collagen C-propeptides, which names human TLL-1 acting on human procollagens I and II. Reason: Procollagen C-propeptide removal by human TLL-1 was shown by Scott et al. 1999 (PMID:10479448), as summarised by Reactome. This is a metalloendopeptidase reaction. Supporting Evidence: Reactome:R-HSA-2002440 TLL-1 (human types I, II, human enzyme, Scott et al. 1999) PMID:10479448 mTLL-1 is shown to specifically process procollagen C-propeptides at the physiologically relevant site |
| GO:0004222 metalloendopeptidase activity | TAS Reactome:R-HSA-2022141 | ACCEPT | Summary: Reactome reaction for pro-lysyl oxidase activation, listing TLL1 among the proteases that cleave proLOX at the physiological site. Reason: Purified recombinant mTLL-1 cleaves pro-lysyl oxidase at the correct physiological site, though about 3-fold less efficiently than BMP-1 (PMID:11313359). Supporting Evidence: PMID:11313359 all four proteinases productively cleave pro-lysyl oxidase at the correct physiological site |
| GO:0004252 serine-type endopeptidase activity | IEA GO_REF:0000117 | REMOVE | Summary: ARBA machine-learned assignment of serine-type endopeptidase activity. Reason: Wrong catalytic class. TLL1 is an astacin-family zinc metalloproteinase: its only protease domain is the peptidase M12A domain with zinc-ligand histidines and a catalytic glutamate, and it has no serine-protease (trypsin-like or subtilisin-like) domain. All biochemical work describes it as a metalloproteinase (PMID:30538173, PMID:18824173). The ARBA rule likely reflects other CUB-domain proteins in the family that are serine proteases. Supporting Evidence: file:human/TLL1/TLL1-uniprot.txt DR Pfam; PF01400; Astacin; 1. PMID:18824173 is a multidomain, zinc endopeptidase of the astacin M12A family |
| GO:0004252 serine-type endopeptidase activity | TAS Reactome:R-HSA-2214330 | REMOVE | Summary: Reactome reaction 'Cleavage of collagen VII NC2 region by BMP1', in which TLL1 is listed as able to substitute for BMP1. Reason: The reaction itself (procollagen VII C-propeptide removal at SYAA|DTAG) is supported for mTLL-1 (PMID:11986329), but it is a metalloendopeptidase reaction. TLL1 has no serine-protease domain, so the serine-type endopeptidase mapping of this Reactome reaction is a catalytic-class error. The correct activity, metalloendopeptidase activity, is already accepted on other rows. Supporting Evidence: PMID:11986329 Mammalian tolloid-like (mTLL)-1 and -2, two other proteases of the astacin enzyme family, were able to process procollagen VII at the same site in vitro. file:human/TLL1/TLL1-uniprot.txt DR Pfam; PF01400; Astacin; 1. |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO mapping from the calcium-binding EGF-like domain signatures. Reason: TLL1 has two calcium-binding EGF-like domains, and calcium affects its quaternary structure: full-length TLL-1 forms a calcium-dependent dimer (PMID:20043912). Calcium binding is structural and modulatory rather than the core activity, and some TLL1 substrate cleavage is calcium-independent (PMID:16507574). Supporting Evidence: PMID:20043912 TLL-1, which has intermediate activity, forms a calcium-ion dependent dimer PMID:16507574 mTLL1 is demonstrated to be independent of Ca2 levels in its ability to cleave some, but not all, substrates |
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic propagation of extracellular localization from PTN000013301. Reason: TLL1 has a signal peptide and is secreted; recombinant human TLL1 was purified from culture medium and its activity measured there (PMID:30538173, PMID:39880331). Its substrates are extracellular precursors. Supporting Evidence: PMID:39880331 TLL1 encodes an extracellular metalloprotease regulating extracellular matrix composition and maintenance. file:human/TLL1/TLL1-uniprot.txt FT SIGNAL 1..30 |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location (Secreted) mapping. Reason: Consistent with the signal peptide and with activity measured in conditioned medium (PMID:39880331). Supporting Evidence: PMID:39880331 An activity assay in the extracellular media of the HEK293-transfected cells |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-2002440 | ACCEPT | Summary: Reactome extracellular location for fibrillar procollagen C-propeptide removal. Reason: Procollagen C-propeptide removal is an extracellular reaction carried out by secreted TLL1. Supporting Evidence: Reactome:R-HSA-2002440 Collagen C-propeptides are cleaved by the tolloid family metalloproteinases |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-2022141 | ACCEPT | Summary: Reactome extracellular location for pro-lysyl oxidase activation. Reason: Pro-lysyl oxidase is cleaved extracellularly after secretion. Supporting Evidence: Reactome:R-HSA-2022141 Lysyl oxidase (LOX) is secreted to the extracellular space in an inactive, proenzyme form (proLOX). |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-2214330 | ACCEPT | Summary: Reactome extracellular location for procollagen VII NC2 cleavage. Reason: Procollagen VII processing takes place extracellularly during anchoring fibril assembly (PMID:11986329). Supporting Evidence: PMID:11986329 It is secreted by keratinocytes as a precursor, procollagen VII, and processed into mature collagen during polymerization of the anchoring fibrils. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-3814820 | ACCEPT | Summary: Reactome extracellular location for perlecan (HSPG2) endorepellin cleavage. Reason: The location is correct for a secreted protease acting on a basement-membrane proteoglycan. The perlecan cleavage itself was not re-verified here (the primary paper is not cached). Supporting Evidence: Reactome:R-HSA-3814820 can liberate LG3 by cleaving endorepellin between Asn4196 and Asp4197. |
| GO:0006508 proteolysis | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO proteolysis from peptidase signatures. Reason: True but uninformative. TLL1 performs limited, site-specific processing of precursor proteins, captured by the accepted protein processing term (GO:0016485), which is_a proteolysis. Supporting Evidence: PMID:10479448 mTLL-1 is shown to specifically process procollagen C-propeptides at the physiologically relevant site |
| GO:0008237 metallopeptidase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO metallopeptidase activity. Reason: True but entailed by the accepted, more specific metalloendopeptidase activity (GO:0004222). Supporting Evidence: PMID:18824173 is a multidomain, zinc endopeptidase of the astacin M12A family |
| GO:0008270 zinc ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO zinc ion binding from the metallopeptidase signature. Reason: The astacin domain binds one catalytic zinc ion through three histidines (UniProt binding sites 240, 244 and 250, PROSITE ProRule PRU01211); the human TLL-1 protease-domain crystal structure was solved (PMID:18824173). Zinc binding is required for catalysis. Supporting Evidence: file:human/TLL1/TLL1-uniprot.txt Note=Binds 1 zinc ion per subunit. PMID:18824173 We report here the crystal structures of the protease domains of human BMP-1 and the closely related Tolloid-like protease 1 (TLL-1). |
| GO:0009953 dorsal/ventral pattern formation | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic propagation of dorsal/ventral pattern formation from the bilaterian tolloid node PTN001298759, seeded by Drosophila tolloid and zebrafish tolloid-family genes. Reason: The mechanism is conserved: TLL1 cleaves chordin, the vertebrate Sog ortholog, and overexpressed TLL-1 counteracts Chordin dorsalisation in Xenopus embryos (PMID:10479448). Products of Bmp1 and Tll1 together account for chordin cleavage in mouse (PMID:12808086). The protease does part of the work by liberating BMP ligands from chordin. However, there is no evidence that TLL1 shapes the mammalian dorsoventral axis; Tll1-null mouse defects are confined to the heart (PMID:10331975), and Scott et al. suggest BMP-1 is the major mammalian chordin antagonist. The IBA is kept as an inherited but non-core role. Supporting Evidence: PMID:10479448 BMP-1 and mTLL-1 are shown to cleave Chordin, at sites similar to procollagen C-propeptide cleavage sites, and to counteract dorsalizing effects of Chordin upon overexpression in Xenopus embryos. PMID:12808086 products of Bmp1 and Tll1 are responsible for in vivo cleavage of Chordin in mammals |
| GO:0016485 protein processing | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic propagation of protein processing from PTN001298759. Reason: Core. TLL1 performs limited, site-specific cleavage of extracellular precursors to their mature forms: procollagen I-III C-propeptides (PMID:10479448, PMID:12808086), pro-lysyl oxidase (PMID:11313359), probiglycan (PMID:10896944), procollagen VII (PMID:11986329) and the myostatin propeptide (PMID:14671324). Supporting Evidence: PMID:12808086 mTLL-1 is an in vivo pCP that provides residual activity observed in Bmp1(-/-) embryos PMID:11313359 the combination of BMP-1/mTLD and mTLL-1 is shown to be responsible for the majority of processing leading to activation of lysyl oxidase by murine embryonic fibroblasts |
| GO:0030199 collagen fibril organization | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learned assignment of collagen fibril organization. Reason: Although the source is an ARBA rule, the term is independently supported. C-propeptide removal is a required step of fibrillar collagen assembly, and TLL1 carries out that step as an in vivo procollagen C-proteinase (PMID:12808086); it also activates lysyl oxidase, which cross-links fibrils (PMID:11313359). Bmp1-null mice have aberrant collagen fibrils with residual pCP activity provided by TLL1. Supporting Evidence: PMID:12808086 although Bmp1(-/-) mice have aberrant collagen fibrils, they have residual pCP activity, indicative of genetic redundancy PMID:12808086 mTLL-1 is an in vivo pCP that provides residual activity observed in Bmp1(-/-) embryos |
| GO:0030199 collagen fibril organization | TAS Reactome:R-HSA-1650814 | ACCEPT | Summary: Reactome pathway 'Collagen biosynthesis and modifying enzymes'. Reason: TLL1 participates by removing procollagen C-propeptides, a step that precedes fibril formation (PMID:10479448, PMID:12808086). Supporting Evidence: Reactome:R-HSA-1650814 which are cleaved prior to formation of the collagen fibril PMID:12808086 mTLL-1 is an in vivo pCP |
| GO:0030199 collagen fibril organization | TAS Reactome:R-HSA-2214320 | ACCEPT | Summary: Reactome pathway 'Anchoring fibril formation' (collagen VII). Reason: mTLL-1 processes procollagen VII at the BMP-1 site in vitro, and is proposed to substitute for BMP-1 in vivo, since Bmp1-null skin still processes procollagen VII (PMID:11986329). The in vivo evidence for TLL1 specifically is indirect. Supporting Evidence: PMID:11986329 deficiency of BMP-1 in the skin of knockout mouse embryos did not prevent processing of procollagen VII to mature collagen, suggesting that mTLL-1 and/or mTLL-2 can substitute for BMP-1 in the processing of procollagen VII in situ |
| GO:0030199 collagen fibril organization | TAS Reactome:R-HSA-2243919 | ACCEPT | Summary: Reactome pathway 'Crosslinking of collagen fibrils', via activation of pro-lysyl oxidase. Reason: TLL1 contributes to fibril cross-linking by activating lysyl oxidase (PMID:11313359), and it also directly processes procollagen, so the process term is supported by its activities. Supporting Evidence: PMID:11313359 Lysyl oxidase catalyzes the final enzymatic step required for collagen and elastin cross-linking in extracellular matrix biosynthesis. |
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Download this section (compressed HTML)Q: Which TLL1 substrate (chordin, a procollagen, or another matrix precursor) explains the interventricular septum defect of Tll1-null mice, given that BMP1 does not compensate there?
Q: Are the procollagen C-proteinase and chordinase activities conserved in non-mammalian TLL1 orthologs inside PTHR24251:SF45, given that the TLL2 paralogs in the same subfamily lack procollagen C-proteinase activity?
Q: Does the truncated isoform 2, which retains the protease domain and CUB1 only, encode an active protease, and is it expressed as protein?
Experiment: Generate a catalytically inactive Tll1 knock-in mouse (active-site glutamate to alanine) and compare cardiac septation with the null allele.
Hypothesis: The cardiac septation defect of Tll1-null mice requires TLL1 protease activity.
Type: knock-in mouse model
Experiment: Use N-terminomics (e.g. TAILS) on matrix from wild-type versus TLL1-deficient cardiac fibroblasts to identify TLL1-specific cleavage sites.
Hypothesis: TLL1 has extracellular substrates in heart tissue that BMP1 does not cleave.
Type: proteomics
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