ENAH Binding to the Huntingtin Proline-Rich Domain Modulates HTT1a Assembly

The proline-rich domain (PRD) of the huntingtin protein (HTT) plays a crucial role in controlling the aggregation and toxicity of mutant HTT1a. To find proteins that interact with the PRD, researchers performed a mass spectrometry analysis of the PRD peptide pull-downs from human neuron samples. ENAH, a protein from the Ena/VASP family involved in actin regulation, was identified as the most abundant interacting protein from these neuronal membrane fractions.

When observed in neurons, ENAH was found to be located alongside HTT1a species, indicating a significant interaction between the two proteins. The EVH1 domain of ENAH has a strong affinity for polyproline motifs, so the researchers investigated its interaction with HTT1a using recombinant proteins. Surprisingly, EVH1 directly bound to HTT1a and formed condensate-like assemblies capable of recruiting HTT1a monomers.

In a remarkable discovery, EVH1 effectively suppressed HTT1a oligomerization and promoted the remodeling of pre-existing HTT1a fibrils in vitro. These findings demonstrate that the interaction between ENAH-PRD modulates the aggregation dynamics of HTT1a, identifying EVH1 assembly as a potential proteostatic mechanism regulating mutant HTT1a states.

This study establishes a framework for understanding how proteins containing EVH1 might influence HTT1a proteostasis and neurotoxicity in Huntington's disease.