Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in the activation domain of a transcription factor

Albert Escobedo, Busra Topal, Micha Ben Achim Kunze, Juan Aranda, Giulio Chiesa, Daniele Mungianu, Ganeko Bernardo­Seisdedos, Bahareh Eftekharzadeh, Margarida Gairí, Roberta Pierattelli, Isabella C. Felli, Tammo Diercks, Oscar Millet, Jesús García, Modesto Orozco, Ramon Crehuet, Kresten Lindorff­Larsen, Xavier Salvatella

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Mar 04, 2019
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Received Date: 13th February 19

Polyglutamine (polyQ) tracts are regions of low sequence complexity of variable length found in more than one hundred human proteins. These tracts are frequent in activation domains of transcription factors and their length often correlates with transcriptional activity. In addition, in nine proteins, tract elongation beyond specific thresholds causes polyQ disorders. To study the structural basis of the association between tract length, transcriptional activity and disease, here we addressed how the conformation of the polyQ tract of the androgen receptor (AR), a transcription factor associated with the polyQ disease spinobulbar muscular atrophy (SBMA), depends on its length. We found that the tract folds into a helical structure stabilized by unconventional hydrogen bonds between glutamine side chains and main chain carbonyl groups. These bonds are bifurcate with the conventional main chain to main chain hydrogen bonds stabilizing α-helices. In addition, since tract elongation provides additional interactions, the helicity of the polyQ tract directly correlates with its length. These findings suggest a plausible rationale for the association between polyQ tract length and AR transcriptional activity and have implications for establishing the mechanistic basis of SBMA

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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