SPRYD3

SPRYD3 functions as a substrate specificity factor within the ubiquitin–proteasome system that controls mitotic cell fate during anti-microtubule drug-induced arrest (PMID:41052634). It associates with the E3 ubiquitin ligase MYCBP2 (PAM) to form a SPRYD3-MYCBP2 ligase complex distinct from the previously characterized FBXO45-MYCBP2 complex (PMID:41052634). This complex ubiquitinates the deubiquitinase USP11 at cysteine 318 through non-canonical ubiquitination, an unusual cooperative arrangement in which an E3 ligase and a DUB act within a single complex (PMID:41052634). Functionally, SPRYD3-MYCBP2-mediated modification of USP11 promotes bipolar spindle formation and facilitates mitotic slippage in cells treated with microtubule-targeting drugs, establishing SPRYD3 as a regulator of mitotic outcome (PMID:41052634).

1. 2025 Medium

   Establishing whether SPRYD3 has a defined biochemical role, this work identified it as a substrate specificity factor partnering MYCBP2 in a ligase complex separate from the known FBXO45-MYCBP2 assembly.

   Evidence Co-immunoprecipitation and complex identification in cell-based experiments

   PMID:41052634

   Open questions at the time

   • Complex identified by Co-IP in a single study without reciprocal structural validation
   • Stoichiometry and architecture of the SPRYD3-MYCBP2 complex not resolved
   • Whether SPRYD3 directs MYCBP2 to additional substrates is unknown
2. 2025 High

   To define the molecular output of the complex, the substrate and modification site were mapped, showing the SPRYD3-MYCBP2 complex ubiquitinates USP11 on cysteine 318 by non-canonical ubiquitination.

   Evidence Ubiquitination assay with site-specific mutagenesis of USP11 C318 and biochemical complex reconstitution

   PMID:41052634

   Open questions at the time

   • Functional consequence of C318 modification on USP11 catalytic activity not fully resolved
   • Whether the ubiquitin chain type/linkage is characterized is not stated
   • Cooperative E3–DUB logic generalizability untested
3. 2025 Medium

   To connect the biochemistry to a cellular phenotype, loss-of-function studies showed the pathway promotes bipolar spindle formation and mitotic slippage under microtubule-targeting drug treatment, placing SPRYD3 as a determinant of mitotic fate.

   Evidence Loss-of-function experiments with anti-microtubule drug treatment, spindle assembly assays, and mitotic fate monitoring

   PMID:41052634

   Open questions at the time

   • Single-lab phenotype not independently replicated
   • Relevance to drug resistance in tumor cells not established
   • Downstream targets of USP11 mediating spindle effects not identified

• Whether SPRYD3 functions beyond the mitotic MYCBP2-USP11 axis and how it selects substrates structurally remain open.
• No structural model of SPRYD3 or its substrate-recognition interface
• No additional substrates or physiological contexts characterized
• Independent confirmation of all findings from a second laboratory absent