Huntington Structure and Function: An Enigma
December 10 - 11, 2000 - Hereditary Disease Foundation / Jennifer Jones Simon Foundation,
Los Angeles, CA
Prepared By Olivier Becker
Abstract
Solution structure of polyglutamine: Does it exist?
According to circular dichroism measurements that Ron Wetzel reported, neither short nor long polyQ peptides assume a stable structure in solution (where "short" and "long" here and elsewhere implies fewer or more Qs, respectively, than the roughly 40 necessary to make huntingtin pathogenic in humans). But antibodies from Paul Patterson's laboratory bind long polyQ preferentially over short polyQ, according to peptide ELISA and Western blots of pathological and benign forms of huntingtin (Htt).
Participants questioned the biological relevance of the ELISA and Western observations when Patterson reported that the antibodies stain wild-type and HD mouse tissue sections at similar intensities. But dissimilarities in the subcellular pattern of staining suggest that the accessibility or conformation of the polyQ tract within Htt depends on context. Structural differences between short and long polyQ exist in vivo, but cellular factors obscure it, Patterson proposed.
To account for antibody preference without presupposing that polyQ naturally assumes a stable structure, participants hypothesized that Patterson's antibodies induce the structure to which they bind. It was proposed that Shiva Malek of Aurora Biosciences should test this hypothesis with a peptide assay that she is developing, with which she hopes to detect conformational changes in polyQ by fluorescence resonance energy transfer.
Participants suggested that the structure that antibodies hypothetically induce might be either a) a fold that polyQ assumes within the context of the Htt protein, or b) a conformation that Htt adopts in transition from soluble to aggregated form.
In light of a), participants suggested that polyQ might fold without antibodies in peptides that that incorporated the immediate flanking sequences from Htt. They proposed engineering such peptides.
Interpretation b) arose from consideration of Htt aggregation in thermodynamic terms, as described below.
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