Interactions between homopolymeric amino acids (HPAAs)

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Human proteins frequently contain homopolymeric amino acid (HPAA) tracts.
• Expanded HPAA tracts are implicated in inherited diseases, including nine polyglutamine and nine polyalanine disorders.
• Polyalanine tracts are linked to pathogenic conditions such as oculopharyngeal muscular dystrophy.

Purpose of the Study:

• To investigate potential interactions between homopolymeric amino acid (HPAA) tracts.
• To elucidate the role of hydrophobicity in HPAA aggregation.
• To understand the molecular mechanisms underlying polyalanine-related diseases.

Main Methods:

• Yeast two-hybrid assays were employed to examine HPAA-HPAA interactions using approximately 30-residue HPAAs.
• COS-7 cells were used to observe HPAA aggregation.
• Polyalanine constructs of varying lengths were tested using yeast two-hybrid and GST pulldown assays.
• SDS-PAGE and native-PAGE assays assessed SDS sensitivity.
• Intracellular localization studies were conducted.

Main Results:

• Hydrophobic HPAAs exhibit self-interaction and interact with other hydrophobic HPAAs.
• Hydrophobic HPAAs form significant aggregates, indicating hydrophobicity's role in aggregation.
• Polyalanine tracts longer than 23 residues demonstrate self-interaction, unlike shorter tracts.
• Polyalanine self-interaction is SDS-sensitive.
• Long polyalanine tracts show disturbed intracellular localization.

Conclusions:

• Long polyalanine tracts acquire SDS-sensitive self-association properties.
• This self-association may be a prerequisite for abnormal protein folding in polyalanine diseases.
• Misfolding of HPAA tracts is a potential common molecular basis for related inherited diseases.