Aggregation of mutant htt

The major goal of this project is to morphologically define the aggregation of expanded polyQ proteins, in particular huntingtin (htt), with a focus on the role of liquid/solid interfaces and protein context. Considering the numerous types of aggregates formed by proteins and peptides containing expanded polyQ tracts that can co-exist, the elucidation of toxic species is a daunting task. The co-existence of diverse aggregate types in heterogeneous mixtures further complicates this issue.

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Huntington’s disease (HD), a fatal neurodegenerative disorder, is caused by an expansion of a polyglutamine (polyQ) tract in the protein huntingtin (htt). This expanded polyQ tract leads to its aggregation into fibrils. This mutational mechanism is also responsible for a growing number of less common neurodegenerative disorders, that include the spinocerebellar ataxias (SCAs). In particular with HD brains, mutant htt is detected predominantly in microscopic inclusion bodies in the cytoplasm and nucleus, but is also found in neurophil associated with microtubules and in many types of membranous organelles, including mitochondria, endoplasmic reticulum, tubulovesicles, endosomes, lysosomes and synaptic vesicles.

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We are obtaining a detailed understanding of the role of flanking sequences in influencing polyQ aggregation and a determination of the interaction of formed aggregates with cellular and subcellular surfaces associated with membranous organelles. Using a combination of ex situ and in situ AFM with other biochemical techniques, we are studying the aggregation of mutant htt exon1 proteins and synthetic polyQ peptides with various lengths of polyQ tracts and flanking sequences. We are able to quantify the relative number of aggregate types formed as a function of time and also gain insight into their interactions with each other and surfaces along the aggregation pathway.