New Transport Control Mechanism Supporting the Formation of the Axon Initial Segment

Research Highlights: The Axon Initial Segment (AIS) of neurons is critical for neural function. We have elucidated the molecular mechanism by which TRIM46, a protein essential for AIS formation, is selectively transported by the motor protein Kinesin-2 (KIF3). Through multidisciplinary analysis, including cell biology, biochemistry, and Small-Angle X-ray Scattering (SAXS), we demonstrated that KIF3/KAP3 complexes exist in multiple compositional patterns, each with distinct cargo specificity. Specifically, we revealed that KIF3B/B/KAP3 is crucial for the transport of TRIM46, which localizes specifically to the AIS. This finding shows that the compositional diversity of Kinesin-2 complexes enables precise intracellular material transport control, contributing to our understanding of neural circuit formation and the molecular basis of neurological diseases. Overview: A research group led by Dr. Nobutaka Hirokawa (Specially Appointed Professor, Juntendo University/Professor Emeritus, University of Tokyo) and others has clarified the molecular mechanism by which TRIM46 is selectively transported by Kinesin-2. Our study shows that KIF3B-containing complexes are essential for the accumulation of TRIM46 at the AIS. Furthermore, using biochemical techniques and SAXS, we discovered that Kinesin-2 complexes exist as multiple subtypes with different compositions, each possessing the ability to selectively transport specific cargo. These results support the conclusion that subtype differentiation of Kinesin-2 complexes serves as the foundation for cargo selectivity and transport control.