MORN2

Model summary

A small human adaptor that uses tandem repeat modules to mediate multivalent protein interactions central to ciliogenesis. By forming a rigid scaffold, it concentrates and stabilizes dynein-arm assembly factors and coordinates their delivery to axonemal building sites. Its association with cytoskeletal frameworks positions preassembled dynein modules and couples them to trafficking routes feeding the basal body, thereby promoting axoneme and outer dynein arm assembly.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The polypeptide is short and entirely covered by IPR052849 (MORN repeat-containing protein family, residues 1–75). Within this, two tandem MORN repeats are annotated: IPR003409 (MORN repeat, residues 13–36) followed by IPR003409 (MORN repeat, residues 36–57). This compact N-terminal-to-C-terminal arrangement—family envelope (IPR052849) containing a dyad of MORN repeats—defines a small, repeat-driven scaffold. MORN repeats are membrane- and cytoskeleton-associated modules that create extended, amphipathic surfaces suited for multivalent binding rather than catalysis. The absence of catalytic signatures and the presence of tandem repeats that expand interaction valency causally point to a non-enzymatic adaptor whose primary chemistry is protein binding, aligning with GO:0005515 protein binding as the molecular function.

2. 02

   From this binding-centric core, I infer the biological role by considering what assembly pathways require multivalent scaffolds.

   The explicit process labels point to ciliogenesis machinery: GO:0035082 axoneme assembly and GO:0036158 outer dynein arm assembly. The tandem MORN scaffold provides the avidity and geometry needed to nucleate and stabilize preassembly complexes of axonemal dynein arms and their adaptors. Such dynein arm assembly modules must be built and handed off to intraflagellar transport pathways; a small, repeat-rich adaptor is well-suited to coordinate this choreography. Thus, the MORN architecture drives selective recruitment and stabilization of dynein-arm components, causally supporting both axoneme assembly and outer dynein arm assembly.

3. 03

   Cellular localization follows from the same scaffold logic and the provided compartmental cues.

   The GO cellular component leaf GO:0045111 intermediate filament cytoskeleton indicates a cytoskeletal neighborhood frequently used as a staging ground for ciliogenesis and vesicle trafficking hubs. A MORN-repeat adaptor that binds cytoskeletal frameworks can spatially organize preassembly of dynein arms and synchronize them with trafficking routes that feed the basal body. This cytoskeletal anchoring explains how the protein concentrates assembly factors and interfaces with transport systems that deliver dynein complexes toward the ciliary base.

4. 04

   Integrating these lines of evidence yields a mechanistic hypothesis.

   The tandem MORN repeats create a small, rigidified platform that captures dynein-arm assembly factors and intermediate filament-associated adaptors. By docking to the intermediate filament cytoskeleton, the protein positions and stabilizes preassembled dynein modules and coordinates their transfer to axonemal building sites. Likely partners include outer dynein arm components and their assembly factors (e.g., DNAH- and DNAI-containing complexes), cytolinker proteins that bridge intermediate filaments and dynein adaptors, and vesicle-trafficking adaptors that deliver cargo to the basal body. This adaptor-centric mechanism accounts for its protein-binding function, its role in axoneme and dynein-arm assembly, and its cytoskeletal residency.