The Effect of Oxidized Dopamine on the Structure and Molecular Chaperone Function of the Small Heat-Shock Proteins, αB-Crystallin and Hsp27

Abstract

Oxidation of the neurotransmitter, dopamine (DA), is a pathological hallmark of Parkinson’s disease (PD). Oxidized DA forms adducts with proteins which can alter their functionality. αB-crystallin and Hsp27 are intracellular, small heat-shock molecular chaperone proteins (sHsps) which form the first line of defense to prevent protein aggregation under conditions of cellular stress. In vitro, the effects of oxidized DA on the structure and function of αB-crystallin and Hsp27 were investigated. Oxidized DA promoted the cross-linking of αB-crystallin and Hsp27 to form well-defined dimer, trimer, tetramer, etc., species, as monitored by SDS-PAGE. Lysine residues were involved in the cross-links. The secondary structure of the sHsps was not altered significantly upon cross-linking with oxidized DA but their oligomeric size was increased. When modified with a molar equivalent of DA, sHsp chaperone functionality was largely retained in preventing both amorphous and amyloid fibrillar aggregation, including fibril formation of mutant (A53T) α-synuclein, a protein whose aggregation is associated with autosomal PD. In the main, higher levels of sHsp modification with DA led to a reduction in chaperone effectiveness. In vivo, DA is sequestered into acidic vesicles to prevent its oxidation and, intracellularly, oxidation is minimized by mM levels of the antioxidant, glutathione. In vitro, acidic pH and glutathione prevented the formation of oxidized DA-induced cross-linking of the sHsps. Oxidized DA-modified αB-crystallin and Hsp27 were not cytotoxic. In a cellular context, retention of significant chaperone functionality by mildly oxidized DA-modified sHsps would contribute to proteostasis by preventing protein aggregation (particularly of α-synuclein) that is associated with PD.

Upregulation of Heat-Shock Protein (hsp)-27 in a Patient with Heterozygous SPG11 c.1951C>T and SYNJ1 c.2614G>T Mutations Causing Clinical Spastic Paraplegia

“…Small heat-shock proteins are well known because their cellular function is to stabilize and prevent protein misfolding and aggregation [41]. A recent study showed that even at low levels of DA ox , the hsp27 activity was significant in preventing amyloid fibrillar and amorphous aggregation of proteins [42]. Thus, we suggest that hsp27 is upregulated as a cellular mechanism of protection and/or to balance impaired protein trafficking.…”

Role of dopamine in the pathophysiology of Parkinson’s disease

“…The DAQ-modified proteins are involved in the DA-induced toxicity to human dopaminergic neurons [ 58 ]. DAQs can conjugate with αB-crystallin and heat shock protein 27 (HSP27), two small heat-shock chaperone proteins, to promote the cross-linking of αB-crystallin and HSP27 and inhibit their chaperone functions [ 59 ]. Moreover, DAQs can inhibit mitochondrial, lysosomal, autophagy and UPS functions in dopaminergic neurons [ 12 , 60 – 62 ].…”

β-Synuclein: An Enigmatic Protein with Diverse Functionality

“…DA is a neurotransmitter which regulates motor function. It is susceptible to oxidation at physiological pH, leading to the formation of highly reactive intermediates such as aminochromes which cross-link and/or inactive proteins [ 60 , 61 ]. Furthermore, oxidized DA has been implicated in mitochondrial and lysosomal dysfunction in PD [ 62 ].…”