Poster Presentation The 44th Lorne Conference on Protein Structure and Function 2019

The molecular chaperone alphaB-crystallin still retains functionality in inhibiting protein aggregation after cross-linking with the oxidative stressor, dopamine (#122)

Junna Hayashi 1 , Daniel Stephens 1 , Thomas Preiss 2 , Dean L Pountney 3 , John A Carver 1
  1. Research School of Chemistry, Australian National University, Canberra, ACT, Australia
  2. John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia
  3. School of Medical Science, Griffith University, Gold Coast, QLD, Australia

Oxidation of the neurotransmitter, dopamine, is a pathological hallmark of Parkinson’s disease. Dopamine oxidation encourages proteins to adopt a neurotoxic conformation, often by forming adducts and thereby reducing their functional activity. αB-crystallin is an intracellular, small heat-shock, molecular chaperone protein, which forms the first line of defence to prevent protein aggregation. However, the effects of oxidised dopamine on the structure and function of αB-crystallin, or other ATP-independent molecular chaperones, have not yet been investigated. Here, we show that oxidised dopamine promotes cross-linking of αB-crystallin. Interestingly, dopamine-modified αB-crystallin was still capable of inhibiting amorphous and fibrillar protein aggregation, including that of mutant of α-synuclein, a protein linked to autosomal Parkinson’s disease. We found that oxidised dopamine induced the formation of larger oligomeric species of αB-crystallin (having a mean diameter of ~ 15 nm compared to ~ 12 nm for non-dopamine treated αB-crystallin) which were SDS and heat resistant, and non-amyloidogenic. The oligomers were more resistant to proteolysis, non-toxic to cells, and did not differ in their exposed hydrophobicity in comparison to their non-modified counterpart. Scavenging of free amino acids and mass spectrometry revealed that oxidised dopamine potentially modified αB-crystallin via its tryptophan, tyrosine and methionine residues. Our results demonstrate that upon modification by dopamine, αB-crystallin retains its chaperone ability at levels comparable to its non-modified equivalent, implying that it is a highly robust molecular chaperone. We anticipate that these results reflect the in vivo environment of the brain, in which although dopamine oxidation mediates the progression of Parkinson’s disease, dopamine modified αB-crystallin can mitigate the neurotoxicity induced by protein aggregation.