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Published on: December 10, 2021
Identification of binding sites in Huntingtin for the Huntingtin Interacting Proteins HIP14 and HIP14L
Shaun S Sanders1, Katherine K N Mui1, Liza M Sutton1
1Department of Medical Genetics and Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada.
Insights
Huntingtin Interacting Protein 14 (HIP14) and HIP14L interact with and palmitoylate Huntingtin (HTT), crucial for Huntington disease. This study identifies specific HTT domains essential for HIP14/HIP14L binding, offering therapeutic targets.
Area of Science:
- Neurodegenerative Diseases
- Molecular Biology
- Protein Biochemistry
Background:
- Huntington disease (HD) is an adult-onset neurodegenerative disorder caused by a CAG expansion in the HTT gene, leading to motor, cognitive, and psychiatric deficits.
- Huntingtin Interacting Protein 14 (HIP14) and HIP14-like (HIP14L) are palmitoyl acyltransferases (PATs) that regulate protein function through palmitoylation.
- HIP14 and HIP14L interact with and palmitoylate HTT, a process impaired in HD, contributing to disease pathology.
Purpose of the Study:
- To elucidate the specific domains within HTT responsible for its interaction with HIP14 and HIP14L.
- To understand how these interactions are affected by deletions within the HTT N- and C-termini.
- To identify potential therapeutic targets for enhancing HIP14/HIP14L activity in Huntington disease.
Main Methods:
- Assessment of HIP14 and HIP14L interaction with various N- and C-terminal deletion mutants of HTT (amino acids 1-548).
- Utilized HIP14-GFP and HIP14L-GFP constructs to analyze binding to a specific HTT mutant (15Q HTT 1-548Δ257-315).
- Investigated the role of ankyrin repeat domains in mediating HIP14/HIP14L and HTT interactions.
Main Results:
- Full interaction between HIP14/HIP14L and HTT requires amino acids 1-548.
- Partial interaction was observed with HTT fragments 1-427 and 224-548, suggesting multiple binding sites.
- Deletion of residues 257-315 in HTT reduced but did not abolish HIP14/HIP14L interaction, indicating these residues are important but not solely responsible for binding.
Conclusions:
- HTT amino acids 1-548 are sufficient for full interaction with HIP14 and HIP14L.
- Two potential binding domains for HIP14 and HIP14L on HTT exist, one near residue 224 and another near residue 427.
- Further characterization of these binding domains is crucial for developing therapeutic strategies to modulate HIP14/HIP14L activity in Huntington disease.
Abstract:
Huntington disease is an adult onset neurodegenerative disease characterized by motor, cognitive, and psychiatric dysfunction, caused by a CAG expansion in the HTT gene. Huntingtin Interacting Protein 14 (HIP14) and Huntingtin Interacting Protein 14-like (HIP14L) are palmitoyl acyltransferases (PATs), enzymes that mediate the post-translational addition of long chain fatty acids to proteins in a process called palmitoylation. HIP14 and HIP14L interact with and palmitoylate HTT and are unique among PATs as they are the only two that have an ankyrin repeat domain, which mediates the interaction between HIP14 and HTT. These enzymes show reduced interaction with and palmitoylation of mutant HTT, leading to increased mutant HTT inclusion formation and toxicity. The interaction between HIP14 and HTT goes beyond that of only an enzyme-substrate interaction as HTT is essential for the full enzymatic activity of HIP14. It is important to further understand and characterize the interactions of HTT with HIP14 and HIP14L to guide future efforts to target and enhance this interaction and increase enzyme activity to remediate palmitoylation of HTT and their substrates, as well as to understand the relationship between the three proteins. HIP14 and HIP14L have been previously shown to interact with HTT amino acids 1-548. Here the interaction of HIP14 and HIP14L with N- and C-terminal HTT 1-548 deletion mutations was assessed. We show that HTT amino acids 1-548 were sufficient for full interaction of HTT with HIP14 and HIP14L, but partial interaction was also possible with HTT 1-427 and HTT 224-548. To further characterize the binding domain we assessed the interaction of HIP14-GFP and HIP14L-GFP with 15Q HTT 1-548Δ257-315. Both enzymes showed reduced but not abolished interaction with 15Q HTT 1-548Δ257-315. This suggests that two potential binding domains exist, one around residues 224 and the other around 427, for the PAT enzymes HIP14 and HIP14L.
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