KIF1A is a kinesin family motor involved in the axonal transport of synaptic vesicle precursors (SVPs) along microtubules (MTs). In humans, more than 10 point mutations inKIF1Aare associated with the motor neuron disease hereditary spastic paraplegia (SPG). However, not all of these mutations appear to inhibit the motility of the KIF1A motor, and thus a cogent molecular explanation for howKIF1Amutations lead to neuropathy is not available. In this study, we established in vitro motility assays with purified full-length human KIF1A and found thatKIF1Amutations associated with the hereditary SPG lead to hyperactivation of KIF1A motility. Introduction of the corresponding mutations into theCaenorhabditis elegans KIF1Ahomologunc-104revealed abnormal accumulation of SVPs at the tips of axons and increased anterograde axonal transport of SVPs. Our data reveal that hyperactivation of kinesin motor activity, rather than its loss of function, is a cause of motor neuron disease in humans.
Preferential beta-hexosaminidase (Hex) A (alpha beta) formation in the absence of beta-Hex B (beta beta) due to heterozygous point mutations present in beta-Hex beta-chain alleles of a motor neuron disease patient.
