MYCBPAP

MYCBPAP is a conserved structural component of the C2a projection of the central apparatus in motile cilia and flagella, where it functions within a scaffold complex with the central-apparatus proteins CFAP65/FAP65, CFAP70/FAP70, and FAP174/MYCBP-1 (PMID:33988244, PMID:39092789, PMID:41724729). Its incorporation into the axoneme is dependent on the C2a projection: in fap70 Chlamydomonas mutants lacking C2a, the MYCBPAP ortholog FAP147 is absent, and it co-immunoprecipitates with FAP70, placing it physically within the FAP70/FAP65/FAP147 complex (PMID:33988244). The MYCBPAP domain (residues 129–639) binds the C-terminus of FAP174 through a broad interfacial contact rather than discrete residues (PMID:41724729). In mammals MYCBPAP is essential for male germ cell differentiation, mediating centrosome–nuclear envelope docking, acrosome biogenesis, manchette organization, and sperm tail assembly; knockout mice are infertile with disrupted centrosome docking and abnormal flagellar biogenesis, and its interactome includes CFAP65, CFAP70, the centrosome-associated protein CCP110, and the ribosome elimination-related protein ARMC3 (PMID:39092789, PMID:39704931). Homozygous loss-of-function variants in MYCBPAP cause asthenoteratozoospermia in humans (PMID:39704931). It was originally identified as a testis-specific, post-meiotically expressed binding partner of the c-Myc-associated protein AMY-1 (PMID:12151104).

1. 2002 Medium

   Establishing the first molecular handle on MYCBPAP, it was identified as a testis-specific binding partner of the c-Myc-associated protein AMY-1, hinting at a role in spermatogenesis.

   Evidence Yeast two-hybrid screen of human testis cDNA with co-localization in 293T/HeLa cells

   PMID:12151104

   Open questions at the time

   • No functional readout beyond expression pattern and binding
   • Cellular role of the AMY-1 interaction undefined
   • Connection to cilia/flagella not yet made
2. 2020 Low

   Localization of MYCBPAP protein to motile cilia connected the testis-expressed protein to the ciliary apparatus.

   Evidence mRNA/protein localization in motile ciliated cells within a multi-gene transcriptional signature study

   PMID:32616903

   Open questions at the time

   • Localization only, no functional consequence for MYCBPAP
   • Sub-axonemal position not resolved
   • No interacting partners identified
3. 2021 High

   Structural and biochemical work placed MYCBPAP/FAP147 as a defined component of the C2a projection of the central apparatus within a FAP70/FAP65/FAP147 complex, defining where the protein sits in the axoneme.

   Evidence Cryo-EM, mass spectrometry of fap70-1 mutant axonemes, and reciprocal Co-IP with HA-FAP70 in Chlamydomonas

   PMID:33988244

   Open questions at the time

   • Stoichiometry and assembly order of the C2a complex unresolved
   • Mammalian role not addressed
   • Direct binding interfaces among subunits not mapped
4. 2024 High

   Mouse knockout and human genetics established MYCBPAP as essential for male fertility, linking its loss to defective centrosome-nuclear envelope docking, acrosome/manchette defects, and sperm tail biogenesis, and tying it to asthenoteratozoospermia.

   Evidence Knockout mice with transgenic rescue, testis proteomics, whole-exome sequencing of human patients, and endogenous co-IP/MS identifying CFAP65, CFAP70, CCP110, and ARMC3

   PMID:39092789 PMID:39704931

   Open questions at the time

   • Mechanism by which MYCBPAP enables centrosome docking unknown
   • Functional significance of CCP110 and ARMC3 interactions not dissected
   • How a central-apparatus protein contributes to acrosome/manchette biology unexplained
5. 2026 Medium

   Domain mapping resolved the molecular basis of MYCBPAP's place in the C2a complex, showing its central domain engages FAP174 through a broad interface.

   Evidence In vitro overlay assay, CABS-Dock docking, molecular dynamics, and alanine mutagenesis of FAP174 in Chlamydomonas

   PMID:41724729

   Open questions at the time

   • Interaction not validated in a reconstituted full complex
   • Functional consequence of disrupting the interface in vivo untested
   • Single-lab in vitro/in silico characterization
6. 2024 Low

   A separate finding implicated MYCBPAP in exosome-mediated synaptic remodeling after ischemic stroke, raising the possibility of a non-ciliary role.

   Evidence BMSC-derived exosome internalization assays and MYCBPAP knockdown loss-of-function in rat neurons and stroke model

   PMID:37423468

   Open questions at the time

   • Single loss-of-function approach without a defined molecular mechanism
   • No pathway placement linking MYCBPAP to synaptic remodeling
   • Relationship to its ciliary/flagellar function unclear

• How MYCBPAP mechanistically couples its central-apparatus scaffolding role to centrosome-nuclear envelope docking and acrosome/manchette assembly in spermatids remains unresolved.
• No mechanistic link between C2a scaffolding and centrosome docking
• Roles of CCP110 and ARMC3 interactions undefined
• Whether the AMY-1 interaction has functional relevance in spermatogenesis unknown