CCDC90B

CCDC90B is a mitochondrial protein that functions as a conserved structural scaffold at the inner mitochondrial membrane, supporting mitochondrial complex integrity and metabolic homeostasis (PMID:30612859, PMID:33089979). It adopts a trimeric head-neck-stalk-anchor architecture, and its head domain—the most widespread head type among a conserved family of prokaryotic and eukaryotic organelle proteins—directly engages the mitochondrial calcium uniporter (MCU) in a manner destabilized by Ca2+ binding (PMID:30612859). CCDC90B forms a hetero-oligomeric coiled-coil complex with its paralog MCUR1 whose stability depends on MCUR1, and loss of this scaffold impairs lipid and amino acid metabolism, establishing the complex as a transmembrane scaffold for mitochondrial protein complex integrity even in systems lacking the uniporter [PMID:bio_10.1101_2025.10.14.682030]. Direct binding of uric acid to CCDC90B drives its cellular accumulation, exacerbating mitochondrial calcium influx and disrupting mitochondrial quality control, with CCDC90B overexpression rescuing stem Leydig cell senescence and restoring testosterone in mice (PMID:42242294).

1. 2019 High

   Establishing the structural architecture of CCDC90B answered how this protein is organized and placed it within a conserved organelle protein family, defining its functional head domain.

   Evidence Crystal structure determination of the human head domain plus sequence analysis

   PMID:30612859

   Open questions at the time

   • Structure of the full-length trimer including neck-stalk-anchor not resolved
   • Functional consequence of the architecture not directly tested for CCDC90B
2. 2019 Medium

   Showing the head domain directly binds MCU and is destabilized by Ca2+ identified the molecular interface coupling CCDC90B to the calcium uniporter, though CCDC90B-specific binding was inferred from its paralog MCUR1.

   Evidence Direct binding assays using MCUR1 as a functional proxy, domain mutagenesis, and structural analysis

   PMID:30612859

   Open questions at the time

   • CCDC90B-MCU binding inferred from MCUR1 paralog rather than measured directly
   • Functional consequence of Ca2+-dependent destabilization on uniporter activity not established
3. 2020 Low

   Localization studies confirmed CCDC90B resides in mitochondria, anchoring later functional work in the correct compartment.

   Evidence Overexpression in 293T cells with immunofluorescence staining

   PMID:33089979

   Open questions at the time

   • Single method on overexpressed protein, no endogenous validation or submitochondrial resolution
   • No functional consequence linked to localization
4. 2025 Medium

   Defining the MCUR1-CCDC90B hetero-oligomeric complex and its MCUR1-dependent stability reframed CCDC90B as a transmembrane metabolic scaffold rather than a uniporter-only accessory, since deletion in uniporter-lacking S. pombe still impaired lipid and amino acid metabolism.

   Evidence Genetic deletion in S. pombe, patient-derived fibroblasts, serum metabolomics, and rescue with human MCUR1 (preprint)

   PMID:bio_10.1101_2025.10.14.682030

   Open questions at the time

   • Not yet peer-reviewed
   • Molecular mechanism by which the scaffold maintains complex integrity unresolved
   • Direct metabolic substrate or pathway target not identified
5. 2026 Medium

   Identifying uric acid as a direct CCDC90B ligand connected the protein to mitochondrial quality control and cellular senescence, providing an in vivo gain-of-function rescue.

   Evidence Single-cell RNA sequencing, direct UA-binding assay, organoid and transgenic mouse models, AAV8 gene-therapy rescue

   PMID:42242294

   Open questions at the time

   • Binding-assay rigor and affinity require full-text confirmation
   • Mechanism linking uric acid binding to calcium influx not resolved
   • Single-lab study without independent replication

• How the CCDC90B-MCUR1 scaffold mechanistically maintains mitochondrial complex integrity and couples to calcium handling and metabolic homeostasis remains unresolved.
• No defined molecular mechanism linking scaffold to specific protein complexes
• Direct CCDC90B-MCU binding never measured independent of MCUR1
• Physiological regulation of CCDC90B abundance beyond uric acid unknown