Protein folding is the process by which polypeptide chains acquire their native three-dimensional structure, which is essential for proper protein function. In neurodegenerative diseases, protein homeostasis (proteostasis) becomes disrupted, leading to misfolding, aggregation, and accumulation of toxic protein species. Understanding protein folding mechanisms is critical for developing therapeutic interventions that target the underlying proteinopathy in diseases such as Alzheimer's disease, Parkinson's disease, ALS, and frontotemporal dementia[1].
Proteins face a fundamental challenge known as the "folding problem." The number of possible conformations a polypeptide chain can adopt is astronomically large (Levinthal's paradox), yet proteins fold to their native state in milliseconds to seconds. This is achieved through:
The cell employs multiple quality control mechanisms to ensure proper protein folding:
| System | Location | Function |
|---|---|---|
| Ribosome-associated quality control | Cytosol | Co-translational monitoring |
| Molecular chaperones | Cytosol/ER | Assist folding, prevent aggregation |
| Unfolded protein response (UPR) | ER | Detect and respond to misfolded proteins |
| Proteostasis network | Throughout cell | Coordinate folding, degradation |
Molecular chaperones, particularly heat shock proteins, play essential roles in protein folding:
The Hsp70 family (including Hsp70 and BiP/Grp78) is central to protein folding homeostasis[2]:
Hsp90 specializes in folding signaling proteins and maintaining metastable proteins[3]:
Small Hsps (HspB1, αB-crystallin/HspB5) prevent aggregation[4]:
The endoplasmic reticulum contains specialized chaperones for secretory and membrane proteins:
The proteostasis network integrates multiple stress response pathways[5]:
In neurodegenerative diseases, the proteostasis network becomes overwhelmed[6]:
In Alzheimer's disease, protein misfolding involves multiple proteins[7]:
α-Synuclein misfolding is central to Parkinson's disease[8]:
TDP-43 aggregation characterizes ALS and most FTD cases[9]:
SOD1 mutations cause familial ALS[10]:
Targeting chaperone systems offers therapeutic potential[11]:
Enhancing protein clearance through autophagy[12]:
Several biomarkers reflect proteostasis impairment [11:1]:
| Biomarker | Disease | Significance |
|---|---|---|
| Hsp70 levels | Various | Chaperone response |
| p-Tau | AD | Tau pathology |
| α-Synuclein | PD | Synucleinopathy |
| Neurofilament light chain (NfL) | Various | Neurodegeneration |
| 14-3-3 proteins | CJD, PD | Protein aggregation |
Protein folding intersects with multiple neurodegenerative mechanisms:
Protein folding dysfunction is a central mechanism in neurodegenerative diseases. The proteostasis network, comprising molecular chaperones, degradation systems, and stress responses, normally maintains protein homeostasis but becomes overwhelmed with age and disease. Understanding these mechanisms provides multiple therapeutic targets, from pharmacologic chaperones to autophagy enhancers. As our understanding of protein folding in the brain improves, targeted interventions to restore proteostasis may offer disease-modifying treatments for currently incurable neurodegenerative conditions.
Recent publications on protein folding mechanisms in neurodegeneration.
Hartl FU, Bracher A, Hayer-Hartl M. Molecular chaperones in protein folding. Science. 2011. ↩︎
Taipale M, Jarosz DF, Lindquist S. HSP90 at the hub of protein homeostasis. Nat Rev Mol Cell Biol. 2010. ↩︎
Haslbeck M, Franzmann T, Weinfurtner D, Buchner J. Some like it hot: the structure and function of small heat-shock proteins. Nat Struct Mol Biol. 2005. ↩︎
Powers ET, Morimoto RI, Dillin A, Kelly JW, Balch WE. Biological and chemical approaches to diseases of proteostasis deficiency. Annu Rev Biochem. 2009. ↩︎
Soto C, Estrada LD. Protein misfolding and neurodegeneration. Arch Neurol. 2008. ↩︎
Selkoe DJ. Alzheimer disease: mechanistic understanding predicts novel therapies. Ann Intern Med. 2004. ↩︎
Spillantini MG, Goedert M. The α-synucleinopathies: Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Ann N Y Acad Sci. 2000. ↩︎
Neumann M, Sampathu DM, Kwong LK, et al. TDP-43 proteinopathy in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Science. 2006. ↩︎
Valentine JS, Doucette PA, Zittin Potter S. Copper-zinc superoxide dismutase and amyotrophic lateral sclerosis. Annu Rev Biochem. 2005. ↩︎
Wiseman RL, Balch WE. A new pharmacology—drugging molecular chaperones for therapeutic benefit. Mol Interventions. 2005. ↩︎
Rubinsztein DC, Codogno P, Levine B. Autophagy modulation as a potential therapeutic target for diverse diseases. Nat Rev Drug Discov. 2012. ↩︎ ↩︎
Aebi M, Hornann H. Quality control in the secretory pathway. J Inherit Metab Dis. 2005. ↩︎