ZMYND19

ZMYND19 (MIZIP) is a MYND zinc-finger protein that functions as a conditionally degraded substrate of the CTLH/GID E3 ubiquitin ligase and, when stabilized, as a negative regulator of mTORC1 signaling at the lysosome (PMID:34647674, PMID:41315365). It was first identified as a cytoplasmic interactor of the C-terminus of melanin-concentrating hormone receptor 1 (MCH-R1), to which it is recruited at the plasma membrane upon receptor co-expression (PMID:12208518), and it additionally binds free α- and β-tubulin through its MYND domain without associating with assembled microtubules (PMID:16039987). Mechanistically, ZMYND19 is recognized by the human GID/CTLH complex: it is captured via the GID4 adaptor despite lacking a canonical Pro/N-end degron (PMID:34647674), and is also targeted through a C-terminal degron read by the Muskelin adaptor, a degradation route tuned by TNF-α and mTOR inhibition (PMID:41648430). When CTLH activity is lost, ZMYND19 escapes degradation and accumulates at lysosome outer membranes, where together with MKLN1 it binds Raptor and RagA/C and blocks the interactions of mTORC1 with Rheb and with its substrates S6K and 4E-BP1, inhibiting mTORC1 at a late activation step independently of the tuberous sclerosis complex and downstream of its lysosomal recruitment (PMID:38746323, PMID:41315365). This places ZMYND19 in a ubiquitin/proteasome-based circuit for rapid tuning of mTORC1 activity and associated processes such as ribosome biogenesis (PMID:41315365, PMID:41648430).

1. 2002 Medium

   Established ZMYND19's first physical partner, linking the orphan protein to G-protein-coupled receptor signaling by showing it binds the MCH-R1 C-terminus and is recruited to the membrane.

   Evidence Yeast two-hybrid, overlay/GST pull-down, and co-IP with localization imaging in HEK-293 cells

   PMID:12208518

   Open questions at the time

   • Functional consequence of the MCH-R1 interaction on receptor signaling not determined
   • Binding shown only in heterologous overexpression
2. 2005 Medium

   Defined the MYND domain as a protein-interaction module by mapping tubulin binding to it, revealing ZMYND19 binds free but not polymerized tubulin.

   Evidence Affinity purification, in vitro GST pull-down, in vivo co-IP, and domain-mapping in human cells

   PMID:16039987

   Open questions at the time

   • Biological role of tubulin binding unresolved — no microtubule phenotype observed
   • Single lab, no orthogonal structural confirmation
3. 2005 Low

   Provided native-tissue context by documenting ZMYND19 distribution and MCH-R1 co-expression in brain, supporting physiological relevance of the interaction.

   Evidence Subcellular fractionation, immunoblotting, and immunofluorescence in mouse brain and rat hippocampal neurons

   PMID:15950311

   Open questions at the time

   • Localization data without demonstrated functional consequence
   • No direct in vivo interaction assay in neurons
4. 2021 High

   Identified ZMYND19 as a bona fide CTLH/GID E3 ligase substrate and showed it is recruited atypically via GID4 without a canonical Pro/N-end degron, expanding the substrate logic of this ligase.

   Evidence In vitro ubiquitination, cross-linking mass spectrometry, cryo-EM, and reconstitution of the hGID complex

   PMID:34647674

   Open questions at the time

   • The actual degron motif on ZMYND19 recognized in this pathway not defined
   • Cellular consequence of ZMYND19 turnover not addressed
5. 2024 Medium

   Connected ZMYND19 turnover to a function by showing that upon CTLH/MAEA loss it accumulates at lysosomes and, with MKLN1, binds Raptor and RagA/C to inhibit mTORC1 at a late, TSC-independent activation step.

   Evidence Genome-wide CRISPR screen, MAEA knockout, co-IP, lysosomal fractionation, and mTORC1 activity assays (preprint)

   PMID:38746323

   Open questions at the time

   • Precise molecular block on mTORC1 not yet defined in this version
   • Preprint stage
6. 2025 High

   Resolved the molecular mechanism of inhibition: stabilized ZMYND19/MKLN1 blocks mTORC1 binding to Rheb and to substrates S6K and 4E-BP1, defining a ubiquitin/proteasome circuit for rapid mTORC1 tuning.

   Evidence CRISPR screen, MAEA knockout, co-IP (Raptor, RagA/C, Rheb), lysosome fractionation, and substrate phosphorylation assays

   PMID:41315365

   Open questions at the time

   • Physiological stimulus that normally stabilizes ZMYND19 to engage this brake not established
   • Structural basis of the Rheb/substrate block unknown
7. 2026 Medium

   Identified a conditional C-degron pathway, showing ZMYND19 is degraded via the Muskelin adaptor of CTLH in a manner tuned by TNF-α and mTOR inhibition, linking ligase regulation to ribosome biogenesis.

   Evidence C-terminal capping stability screen, genetic/proteomic screens, CTLH/Muskelin knockout, and proteasome inhibitor assays (preprint)

   PMID:41648430

   Open questions at the time

   • Signal transduction linking TNF-α/mTOR status to degron recognition unresolved
   • Preprint; ribosome biogenesis link not mechanistically detailed

• How ZMYND19's early-characterized roles (MCH-R1 binding, free-tubulin binding) integrate with its lysosomal mTORC1-regulatory function remains unknown.
• Whether MCH-R1 or tubulin binding modulates ZMYND19 stability or mTORC1 inhibition is untested
• No structural model of ZMYND19 itself
• Endogenous physiological trigger for the mTORC1 brake undefined