Final answer:
The elongated sequence of glutamine residues at the Huntingtin protein's N-terminus is key to its toxic pathogenesis in Huntington's disease, which can disrupt cellular processes and lead to neuron death.
Step-by-step explanation:
The key part of the Huntingtin protein involved in its toxic pathogenesis in Huntington's disease is an elongated sequence of glutamine residues located at the protein's N-terminus. This expansion leads to the production of a mutated protein which can disrupt cellular processes. One proposed mechanism of neuron death involves dysregulation in the expression of NMDA receptors, particularly at extrasynaptic sites. Elevated intracellular calcium through these receptors can initiate detrimental cascades, such as mitochondrial membrane potential disruption and neuron death, contributing to the neurological decline seen in this disease.