Abrogation of prenucleation, transient oligomerization of the Huntingtin exon 1 protein by human profilin I.
Proc Natl Acad Sci U S A
; 117(11): 5844-5852, 2020 03 17.
Article
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| MEDLINE
| ID: mdl-32127471
ABSTRACT
Human profilin I reduces aggregation and concomitant toxicity of the polyglutamine-containing N-terminal region of the huntingtin protein encoded by exon 1 (httex1) and responsible for Huntington's disease. Here, we investigate the interaction of profilin with httex1 using NMR techniques designed to quantitatively analyze the kinetics and equilibria of chemical exchange at atomic resolution, including relaxation dispersion, exchange-induced shifts, and lifetime line broadening. We first show that the presence of two polyproline tracts in httex1, absent from a shorter huntingtin variant studied previously, modulates the kinetics of the transient branched oligomerization pathway that precedes nucleation, resulting in an increase in the populations of the on-pathway helical coiled-coil dimeric and tetrameric species (τex ≤ 50 to 70 µs), while leaving the population of the off-pathway (nonproductive) dimeric species largely unaffected (τex â¼750 µs). Next, we show that the affinity of a single molecule of profilin to the polyproline tracts is in the micromolar range (Kdiss â¼ 17 and â¼ 31 µM), but binding of a second molecule of profilin is negatively cooperative, with the affinity reduced â¼11-fold. The lifetime of a 11 complex of httex1 with profilin, determined using a shorter huntingtin variant containing only a single polyproline tract, is shown to be on the submillisecond timescale (τex â¼ 600 µs and Kdiss â¼ 50 µM). Finally, we demonstrate that, in stable profilin-httex1 complexes, the productive oligomerization pathway, leading to the formation of helical coiled-coil httex1 tetramers, is completely abolished, and only the pathway resulting in "nonproductive" dimers remains active, thereby providing a mechanistic basis for how profilin reduces aggregation and toxicity of httex1.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Exones
/
Enfermedad de Huntington
/
Profilinas
/
Proteína Huntingtina
Límite:
Humans
Idioma:
En
Revista:
Proc Natl Acad Sci U S A
Año:
2020
Tipo del documento:
Article