| MICALL1, also referred to as MIRAB13 or molecule interacting with Rab13, is a cytoplasmic MICAL‑family effector that localizes predominantly to the cytosolic face of recycling and late endosome membranes and functions in lipid‑dependent control of endocytic recycling, cargo trafficking, and membrane tubulation. The protein contains an N‑terminal calponin homology domain, a LIM zinc‑binding region, central proline‑rich and coiled‑coil segments, and a C‑terminal Rab‑binding region, and shows phosphatidic acid‑binding activity that favors recycling endosome lipids, together with small GTPase‑binding activity toward Rab proteins. MICALL1 interacts directly with GTP‑bound Rab13 and shares overall domain organization with MICAL proteins; calponin homology and Rab13‑binding regions form an intramolecular contact that is sensitive to Rab13, and disruption of this contact by GTP‑Rab13 correlates with a conformational change that exposes effector interfaces and positions MICALL1 on late endosomal membranes. On endosomal membranes MICALL1 functions as a downstream effector of Rab35, Rab13, and related small GTPases and binds phosphatidic acid‑rich domains, where it organizes multi‑protein assemblies with EHD1 and other cytosolic partners to support membrane tubulation, endosomal carrier formation, and cargo sorting. MICALL1 participates in a late step of receptor‑mediated endocytosis and regulates trafficking of the epidermal growth factor receptor, with MICALL1 enrichment on late endosomes associated with EGFR accumulation in this compartment and MICALL1 depletion associated with dispersed internalized EGFR and enhanced receptor degradation, indicating a defined role in late endocytic trafficking and sorting decisions. MICALL1 also contributes to slow endocytic recycling of internalized proteins back to the plasma membrane and to cargo delivery to the cell surface, functions that place the protein within recycling endosome pathways that control steady‑state receptor and adhesion molecule display and thereby influence cell polarity and signaling responsiveness. MICALL1 recruits EHD1 to primary cilia and associates with tubulin at centrioles, coordinating ciliogenesis and functioning as part of a ciliary trafficking module that connects endosomal recycling with primary cilium formation and maintenance. |
