The Novel KIF1A Missense Variant (R169T) Strongly Reduces Microtubule Stimulated ATPase Activity and is Associated with NESCAV Syndrome

KIF1A is a neuron-specific molecular motor that functions include transporting vesicles along microtubules in a plus end direction, and proper activity of this motor is essential for higher brain function.  Several pathogenic variants of KIF1A have been identified and linked to clinical neurologic disorders, such as, spastic paraplegia and neurodegeneration and spasticity with or without cerebellar atrophy or cortical visual impairment (NESCAV). Interestingly, NESCAV syndrome is strongly linked to de novo missense variants located in the motor domain (aa 1-361) of KIF1A.  Recently, Cinthia Aguilera and colleagues identified a novel missense variant R169T in KIF1A from a patient that presented clinical features that aligned with NESCAV.  Molecular studies determined that this point mutation had no effect on KIF1A protein levels.  However, it had a profound effect on its microtubule-stimulated ATPase activity; whereby, the R169T mutation suppressed ATPase rate by nearly 180-fold.  Significantly higher amounts of microtubules were needed for R169T KIF1A to produce any measurable ATPase activity.  Modeling studies were performed to explain this significant loss in activity, and it was determined that this mutation resides in the b5-loop of the protein, which is one of 3 microtubule binding regions in KIF1A, and revealed that the mutation led to unfavorable electrostatic interactions and diminished binding.  Cytoskeleton’s Kinesin ATPase Endpoint Assay Biochem Kit (Cat. # BK053) was essential to measure R169T KIF1A microtubule-stimulated ATPase activity.  Identification and characterization of KIF1A neuropathological mutations may lead to a better understanding of how they impact proper neuronal development.