CFAP298

CFAP298 is a cytoplasmic axonemal dynein preassembly factor required for the folding and stabilization of axonemal dynein heavy chains, and thereby for the construction of motile cilia (PMID:36026524). Acting at early steps of the preassembly pathway, it associates with nearly all dynein heavy chains (but not the intermediate chains IC1/IC2) and with multiple dynein assembly factors (DNAAFs), and engages the RuvBL1/RuvBL2 chaperone components without binding the holo-R2TP complex; its loss destabilizes dynein heavy chains and disrupts their cytoplasmic assembly with intermediate and light chains, causing loss of both outer and inner dynein arms (PMID:36026524, PMID:40106351). Its activity depends on a structurally defined ubiquitin-like domain within a bilobed architecture, mutation of which abolishes function (PMID:40106351). In vivo, loss of CFAP298 function impairs cilia motility, producing defective left-right axis establishment and disrupted cerebrospinal fluid flow that leads to spine deformities resembling adolescent idiopathic scoliosis (PMID:33795825, PMID:40955177).

1. 2022 High

   Established CFAP298 as a cytoplasmic factor acting early in axonemal dynein preassembly rather than within the axoneme itself, defining its molecular role as folding/stabilization of dynein heavy chains.

   Evidence Comparative proteomics, co-IP/pulldown, fractionation and EM of axonemes in a Chlamydomonas FBB18 loss-of-function mutant

   PMID:36026524

   Open questions at the time

   • Does not resolve the structural basis of heavy chain stabilization
   • Direct versus indirect nature of the many DNAAF/heavy chain associations not dissected
   • Significance of RuvBL1/2 binding without holo-R2TP unexplained
2. 2021 Medium

   Linked CFAP298 loss to an organismal disease phenotype, showing that defective cilia motility and impaired CSF circulation produce scoliosis-like spine deformities.

   Evidence Zebrafish cfap298 (kurly) loss-of-function mutant analyzed by micro-CT of the spine

   PMID:33795825

   Open questions at the time

   • Single model organism and single lab
   • Mechanistic chain from dynein defect to spine curvature not fully reconstructed
3. 2025 High

   Resolved the protein architecture, revealing a bilobed structure with a ubiquitin-like domain that is indispensable for function, and confirmed the cytoplasmic preassembly role through disrupted heavy chain–intermediate/light chain association.

   Evidence X-ray crystallography, ubiquitin-like domain mutagenesis, and biochemical fractionation in Chlamydomonas loss-of-function mutants

   PMID:40106351

   Open questions at the time

   • Molecular mechanism by which the ubiquitin-like domain promotes folding is unknown
   • Whether the domain mediates protein–protein contacts or a chaperone-like activity not determined
4. 2025 Medium

   Defined a conserved protein region required specifically for cilia motility and left-right patterning, separable from effects on cilia position, length, or planar cell polarity.

   Evidence Mouse knock-in allele with live tracheal cilia imaging, PCP marker IF, Nodal/Pitx2/Lefty1 analysis, and cross-species zebrafish rescue

   PMID:40955177

   Open questions at the time

   • Single lab
   • How the deleted region maps onto the ubiquitin-like domain function is not integrated
   • Mechanistic link between the region and dynein assembly not established

• How CFAP298 mechanistically stabilizes dynein heavy chains and coordinates with the broader chaperone/DNAAF machinery remains unresolved.
• No reconstituted biochemical assay of the folding/stabilization activity
• Functional meaning of RuvBL1/2 association without holo-R2TP unknown
• Spectrum of human disease alleles not characterized in this corpus