Therapeutic potential of archaeal unfoldase PANet and the gateless T20S proteasome in P23H rhodopsin retinitis pigmentosa mice.

Neurodegenerative diseases are characterized by the presence of misfolded and aggregated proteins which are thought to contribute to the development of the disease. In one form of inherited blinding disease, retinitis pigmentosa, a P23H mutation in the light-sensing receptor, rhodopsin causes rhodopsin misfolding resulting in complete vision loss. We investigated whether a xenogeneic protein-unfolding ATPase (unfoldase) from thermophilic Archaea, termed PANet, could counteract the proteotoxicity of P23H rhodopsin.

Occupancy of the HbYX hydrophobic pocket is sufficient to induce gate opening in the archaeal 20S proteasomes.

Enhancing proteasome function has been a long-standing but challenging target of interest for the potential treatment of neurodegenerative diseases, emphasizing the importance of understanding proteasome activation mechanisms. Most proteasome activator complexes use the C-terminal HbYX motif to bind and trigger gate-opening in the 20S proteasome. This study defines a critical molecular interaction in the HbYX mechanism that triggers gate opening.

High resolution structures define divergent and convergent mechanisms of archaeal proteasome activation.

Considering the link between neurodegenerative diseases and impaired proteasome function, and the neuro-protective impact of enhanced proteasome activity in animal models, it's crucial to understand proteasome activation mechanisms. A hydrophobic-tyrosine-any residue (HbYX) motif on the C-termini of proteasome-activating complexes independently triggers gate-opening of the 20S core particle for protein degradation; however, the causal allosteric mechanism remains unclear. Our study employs a structurally irreducible dipeptide HbYX mimetic to investigate the allosteric mechanism of gate-opening in the archaeal proteasome.

Minimal mechanistic component of HbYX-dependent proteasome activation that reverses impairment by neurodegenerative-associated oligomers.

The implication of reduced proteasomal function in neurodegenerative diseases combined with studies showing the protective effects of increasing proteasome activity in animal models highlight the need to understand the capacity for proteasome activation by small molecules. The C-terminal HbYX motif is present on many proteasome binding proteins and functions to tether activators to the 20S core particle. Previous studies have shown that peptides with a HbYX motif can autonomously activate 20S gate-opening to allow protein degradation.

Minimal mechanistic component of HbYX-dependent proteasome activation.

The implication of reduced proteasomal function in neurodegenerative diseases combined with numerous studies showing the protective effects of increasing proteasome activity in animal models justify the need to understand how the proteasome is activated for protein degradation. The C-terminal HbYX motif is present on many proteasome binding proteins and functions to tether activators to the 20S core particle. Peptides with a HbYX motif can also autonomously activate 20S gate-opening to allow protein degradation, but the underlying allosteric molecular mechanism is not clear.