| Category | Key points | Best supporting citations |
|---|---|---|
| Enzyme activity / substrate | - tpp1 encodes lysosomal tripeptidyl-peptidase 1 (EC 3.4.14.9), a sedolisin-family serine protease that acts mainly as an **N-terminal exopeptidase** releasing tripeptides, with limited endopeptidase activity.<br>- Conserved catalytic residues reported for zebrafish/homologous TPP1 include **Glu, Asp, Ser**; zebrafish protein is homologous to human TPP1 and was assayed with the fluorogenic substrate **Arg-Ala-Phe-ACC**.<br>- In zebrafish mutants, Tpp1 activity is significantly reduced in embryo extracts, supporting true loss of enzymatic function. | (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000004) |
| Processing & localization | - Zebrafish Tpp1 is a **557 aa** precursor encoded by **13 exons** and is predicted to enter the secretory pathway via a **19 aa signal peptide** before lysosomal delivery.<br>- TPP1 is synthesized as a ~**66–68 kDa precursor** and processed to a ~**46–48 kDa mature enzyme**; trafficking is via the **mannose-6-phosphate** pathway in vertebrate TPP1 literature.<br>- Mahmood et al. note maternally derived Tpp1 persists in lysosomes early, whereas a zygotically derived mutant product lacking signal sequence would fail to reach lysosomes. | (pqac-00000000, pqac-00000001, pqac-00000002) |
| Zebrafish LOF phenotypes & biomarkers | - Homozygous **tpp1sa0011** zebrafish show early progressive neurodegeneration: small retina/head, curved body, absent swim bladder, retinal/cerebellar/tectal defects, axon disorganization, and motor decline.<br>- Quantifiable disease biomarkers include **SCMAS accumulation**, **hypertrophic/enlarged lysosomes**, localized **TUNEL-positive apoptosis**, reduced proliferation in retina and midbrain-hindbrain boundary, and seizure-like hyperactivity preceding motor failure.<br>- Survival is markedly shortened: mutants die around **5 dpf** in the main phenotype summary, with survival curves showing death by about **8 dpf**. | (pqac-00000000, pqac-00000005, pqac-00000006, pqac-00000007, pqac-00000021) |
| Assays | - Enzyme assay conditions in zebrafish embryos: homogenates in acidic buffer (**150 mM NaCl, 100 mM sodium citrate, 1 g/L Triton X-100, pH 4.0**); **6 µg** crude protein incubated with **0.25 mM Arg-Ala-Phe-ACC** in **50 µL** for **90 min**.<br>- Additional functional/pathology assays: RT-PCR genotyping/splice analysis, Western blot, anti-TPP1 immunofluorescence, **LysoTracker** for lysosomal enlargement, **SCMAS** staining, **TUNEL**, and automated locomotor tracking.<br>- Recent zebrafish screening work adds **Lamp1 lysosomal reporters**, EEG for epileptiform activity, RNA-seq, and high-content imaging. | (pqac-00000001, pqac-00000004, pqac-00000005, pqac-00000021) |
| Applications / therapeutics | - Zebrafish tpp1 mutants are used as a **CLN2/Batten disease model** for mechanistic study and whole-organism drug screening because early seizure-like and neurodegenerative phenotypes are machine-quantifiable.<br>- A 640-compound zebrafish screen identified **pregnenolone** as a candidate that suppresses seizures and cell death and improves lysosomal architecture (preprint evidence).<br>- In human CLN2 translational work, CNS-directed **cerliponase alfa** slows neurologic decline but does **not adequately prevent retinal degeneration**; a first-in-human retinal approach used **intravitreal rhTPP1 0.2 mg in 0.05 mL**, unilateral, every 8 weeks / over 12–18 months in 8 children. | (pqac-00000005, pqac-00000008, pqac-00000009, pqac-00000014, pqac-00000015) |
| Key quantitative data | - Identity/structure: **62% identity**, **67% homology** to human TPP1; **557 aa** protein; **13 exons**; **19 aa** signal peptide; mature human/vertebrate TPP1 half-life reported as ~**20 h**.<br>- Zebrafish phenotype timing: pathology detectable from **2 dpf** in later work; progressive eye defects by larval stages; death by **5–8 dpf** depending on readout/study panel.<br>- Human therapeutic numbers: intravitreal rhTPP1 trial enrolled **8 children aged 5–9 years**; PMV decline in progressing patients averaged **0.168 mm3/yr treated vs 0.254 mm3/yr untreated**; cerliponase alfa safety data in **38 children** showed **convulsion-related events in 31/38 (82%)**, only **4%** considered drug-related, and **hypersensitivity in 19/38 (50%)** with **6 grade-3** reactions. | (pqac-00000002, pqac-00000006, pqac-00000008, pqac-00000009, pqac-00000012) |


*Table: This table condenses the most relevant functional annotation points for Danio rerio tpp1/TPP1, including enzyme function, lysosomal localization, zebrafish loss-of-function phenotypes, assays, and translational therapeutic context. It is useful as a quick evidence-linked summary for annotation and disease-model interpretation.*