Affinage

TSSK2

Testis-specific serine/threonine-protein kinase 2 · UniProt Q96PF2

Length
358 aa
Mass
40.9 kDa
Annotated
2026-06-10
12 papers in source corpus 8 papers cited in narrative 8 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TSSK2 is a testis-specific serine/threonine protein kinase that is individually essential for sperm motility, sperm number, and male fertility (PMID:40305308). Recombinant human TSSK2 is enzymatically active with a low ATP Km and is potently inhibited by staurosporine and by pyrrolopyrimidine/pyrimidine small molecules at sub-100 nM potency (PMID:26777341, PMID:28952188). Its identified substrates include the axoneme central-apparatus protein SPAG16L, which it binds via the SPAG16L C-terminal WD-repeat domain and phosphorylates in vitro, and the N-terminal region (aa 1–150) of TSKS (PMID:18367677, PMID:26777341); TSSK2 protein is markedly reduced in SPAG16L-null testes, indicating that the interaction also stabilizes TSSK2 (PMID:18367677). In elongating spermatids TSSK2 is a component of the late chromatoid body, where it associates with translation initiation factors and ribosomal proteins and co-precipitates a defined set of polysome-enriched mRNAs, linking the kinase to temporally regulated translation during late spermatogenesis (PMID:41042594). Genetic ablation produces sterile males with reduced and poorly motile sperm, and acute PROTAC-mediated degradation of TSSK2 in ex vivo sperm collapses motility and fertilizing capacity within hours, establishing that ongoing TSSK2 kinase activity is required for sperm function (PMID:40305308, PMID:42228803).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2008 High

    Established the first molecular substrate and binding partner of TSSK2, connecting the kinase to the sperm axoneme.

    Evidence Yeast two-hybrid, reciprocal Co-IP, in vitro kinase assay, domain mapping, and KO mouse immunoblot identifying SPAG16L

    PMID:18367677

    Open questions at the time
    • Phosphosite on SPAG16L not mapped
    • Functional consequence of SPAG16L phosphorylation in vivo not tested
  2. 2012 Low

    Defined the subcellular distribution of TSSK2 in mature sperm and distinguished it from TSSK1.

    Evidence Immunofluorescence of non-capacitated, capacitated, and acrosome-reacted mouse and human sperm

    PMID:22855445

    Open questions at the time
    • No functional consequence directly tied to TSSK2 localization
    • Species difference (post-acrosomal vs equatorial) unexplained
  3. 2012 Low

    Addressed whether TSSK2 and its paralog TSSK1B are functionally redundant by comparing selective pressures and a human variant.

    Evidence Comparative primate genomics with functional mutagenesis of the K27R variant

    PMID:23258646

    Open questions at the time
    • K27R mutagenesis lacks a described biochemical readout
    • Differential function inferred from evolution, not directly demonstrated
  4. 2016 High

    Confirmed TSSK2 is an active kinase with defined substrates and kinetics, mapping its primary site on TSKS.

    Evidence Baculovirus-expressed recombinant human TSSK2, in vitro kinase assays, TSKS fragment phosphorylation mapping, ATP Km and staurosporine IC50 determination

    PMID:26777341

    Open questions at the time
    • Physiological role of TSKS phosphorylation not established
    • No structural model of the active kinase
  5. 2017 Medium

    Demonstrated TSSK2 is a chemically tractable target and profiled inhibitor selectivity across TSSK isoforms.

    Evidence High-throughput mobility-shift screen of ~17,000 compounds with IC50 profiling across TSSK1/2/3/6

    PMID:28952188

    Open questions at the time
    • Inhibitor activity in sperm not tested in this study
    • Selectivity against the broader kinome not reported
  6. 2025 High

    Established that TSSK2 is individually essential for male fertility, independent of TSSK1.

    Evidence CRISPR/Cas9 knockout mice, mating and IVF fertility assays, sperm count and motility analysis, validated-antibody immunofluorescence

    PMID:40305308

    Open questions at the time
    • Molecular cause of the motility/count defect not resolved
    • Stage at which spermatogenesis fails not pinpointed
  7. 2025 Medium

    Placed TSSK2 in the late chromatoid body and linked it to temporally regulated mRNA translation in elongating spermatids.

    Evidence Protein and RNA interaction profiling, polysome fractionation, late-CB marker co-localization

    PMID:41042594

    Open questions at the time
    • Whether TSSK2 kinase activity controls the associated translation not shown
    • Identity of functionally relevant mRNA targets not validated
  8. 2026 High

    Showed that acute, post-developmental loss of TSSK2 protein is sufficient to abolish sperm motility and fertilization, validating it as a non-hormonal contraceptive target.

    Evidence PROTAC-mediated degradation in ex vivo mouse sperm with HiBiT quantification, motility and IVF readouts

    PMID:42228803

    Open questions at the time
    • Reversibility and in vivo efficacy not addressed
    • Mechanism linking acute kinase loss to motility collapse not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How TSSK2 kinase activity mechanistically couples its substrates (SPAG16L, TSKS) and its chromatoid-body translational role to sperm motility remains unresolved.
  • No in vivo phosphosite-mutant rescue connecting substrate phosphorylation to motility
  • Causal link between late-CB translation and the knockout phenotype untested
  • Structure of TSSK2 and its substrate-recognition basis unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 3 GO:0016740 transferase activity 2 GO:0003723 RNA binding 1
Localization
GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-1474165 Reproduction 2 R-HSA-8953854 Metabolism of RNA 1
Partners
SPAG16LTSKS
Complex memberships
late chromatoid body

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 TSSK2 physically interacts with the axoneme central apparatus protein SPAG16L via the C-terminal WD-repeat domain of SPAG16L; the N-terminal coiled-coil domain does not associate with TSSK2. TSSK2 phosphorylates SPAG16L in vitro, identifying SPAG16L as a TSSK2 substrate. Additionally, TSSK2 protein is absent or markedly reduced in testes of SPAG16L-null mice. Yeast two-hybrid screen, co-immunoprecipitation from testis extracts and co-expressing cell lysates, confocal colocalization, in vitro kinase assay, domain-mapping experiments, immunoblot of knockout mouse testes Biology of reproduction High 18367677
2016 Recombinant human TSSK2 produced in baculovirus is enzymatically active, phosphorylating hTSKS isoform 2, casein, and glycogen synthase peptide in vitro. The N-terminal region (aa 1–150) of TSKS is particularly strongly phosphorylated, localizing the primary TSSK2 phosphorylation site to the N-terminus of human TSKS. ATP Km is ~2.2–2.7 µM; staurosporine inhibits hTSSK2 with IC50 = 20 nM. Baculovirus expression, IMAC and gel-filtration purification, in vitro kinase assay, mobility shift assay, TSKS fragment phosphorylation mapping Protein expression and purification High 26777341
2017 High-throughput mobility-shift kinase assay identified pyrrolopyrimidine and pyrimidine inhibitors of TSSK2 with sub-100 nM potency (best IC50 values: 22 nM and 31 nM). Compound 19 displayed selectivity rank order TSSK1 > TSSK2 > TSSK3 > TSSK6, demonstrating that potent dual TSSK1/2 inhibitors can be identified and that TSSK2 is an inhibitable serine/threonine kinase. High-throughput mobility shift assay (~17,000 compounds), IC50 determination across TSSK isoforms ChemMedChem Medium 28952188
2012 Functional analysis of TSSK2 replacement mutation K27R (frequently observed in humans) was performed; the C-terminal domain of TSSK1B (but not TSSK2) shows evidence of positive selection in primates, suggesting TSSK1B and TSSK2 perform at least partly differential functions. The kinase domains of both TSSK1B and TSSK2 evolved under negative (purifying) selection, consistent with requirement to maintain kinase activity. Evolutionary sequence analysis with functional mutagenesis of K27R variant; comparative genomics in primates Andrology Low 23258646
2012 Immunofluorescence localization of TSSK2 in mouse sperm showed predominant distribution in the post-acrosomal region, while in human sperm TSSK2 was found in the equatorial region. TSSK2 distribution was unchanged after acrosome reaction, distinguishing it from TSSK1. Western blot (mature mouse and human sperm), immunofluorescence on non-capacitated, capacitated, and acrosome-reacted sperm Dong wu xue yan jiu = Zoological research Low 22855445
2025 CRISPR/Cas9-generated Tssk2 homozygous mutant male mice are sterile with lower sperm numbers and decreased motility, establishing that TSSK2 is individually essential for male reproduction independently of TSSK1. Anti-TSSK2 antibodies validated against Tssk2 mutants confirmed TSSK2 localization to the sperm head; TSSK2 is present in testes and sperm of Tssk1 mutant mice, confirming independent function. CRISPR/Cas9 knockout mouse generation, natural mating fertility assay, in vitro fertilization, sperm count and motility analysis, Western blot, immunofluorescence with validated antibody Biomolecules High 40305308
2025 TSSK2 is a component of the late chromatoid body (late-CB) in elongating spermatids. Proteomics and RNA-interaction studies showed TSSK2 associates with translation initiation factors and ribosomal proteins, and co-precipitates a specific set of mRNAs that are enriched in polysome fractions in elongating spermatids, linking the late-CB and TSSK2 to temporally regulated translation during late spermatogenesis. Identification of TSSK2-interacting proteins and RNAs (RNP pulldown/mass spectrometry implied), polysome fractionation, late-CB marker co-localization Reproduction (Cambridge, England) Medium 41042594
2026 Targeted degraders (PROTACs) directed against TSSK2 reduced TSSK2 protein levels by up to 80% in ex vivo mouse sperm within 4 hours, causing a 97% reduction in sperm motility and near-complete loss of in vitro fertilization capacity, demonstrating that acute loss of TSSK2 kinase is sufficient to abrogate sperm motility and fertilizing ability. Targeted protein degrader (PROTAC) treatment of ex vivo CD1 mouse sperm, quantitative Western blot (HiBiT), sperm motility assay, in vitro fertilization assay Journal of medicinal chemistry High 42228803

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2020 Effects of Qilin pills on spermatogenesis, reproductive hormones, oxidative stress, and the TSSK2 gene in a rat model of oligoasthenospermia. BMC complementary medicine and therapies 25 32046715
2008 Phosphorylation of mouse sperm axoneme central apparatus protein SPAG16L by a testis-specific kinase, TSSK2. Biology of reproduction 25 18367677
2009 Some single-nucleotide polymorphisms of the TSSK2 gene may be associated with human spermatogenesis impairment. Journal of andrology 20 19926886
2017 Potent Pyrimidine and Pyrrolopyrimidine Inhibitors of Testis-Specific Serine/Threonine Kinase 2 (TSSK2). ChemMedChem 19 28952188
2012 Evolution of testis-specific kinases TSSK1B and TSSK2 in primates. Andrology 15 23258646
2021 Long Noncoding RNA lnc-TSSK2-8 Activates Canonical Wnt/β-Catenin Signaling Through Small Heat Shock Proteins HSPA6 and CRYAB. Frontiers in cell and developmental biology 9 34041241
2016 Recombinant production of enzymatically active male contraceptive drug target hTSSK2 - Localization of the TSKS domain phosphorylated by TSSK2. Protein expression and purification 7 26777341
2025 Identification of TSSK1 and TSSK2 as Novel Targets for Male Contraception. Biomolecules 5 40305308
2024 CRISPR/Cas9 mediated validation of spermatogenesis-related gene, tssk2 as a component of genetic pest management of fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Archives of insect biochemistry and physiology 4 38783691
2012 [Cloning and expression of Tssk1 & Tssk2 in mice and the presence & localization of them in mature sperm]. Dong wu xue yan jiu = Zoological research 3 22855445
2026 Development of TSSK1 and TSSK2 Targeted Degraders Reveals Sperm Machinery for Protein Degradation and Potential for Nonhormonal Male Contraception. Journal of medicinal chemistry 0 42228803
2025 The late chromatoid body component TSSK2 is involved in translational regulation in elongating spermatids in mice. Reproduction (Cambridge, England) 0 41042594

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