Alvarez-Castelao Beatriz, Goethals Marc, Vandekerckhove Joël, Castaño José G
Departamento de Bioquímica, Instituto de Investigaciones Biomédicas "Alberto Sols", UAM-CSIC y Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain.
Department of Biochemistry, Ghent University, Ghent, Belgium; Department of Medical Protein Research, VIB, Ghent Univeristy, Ghent, Belgium.
Biochim Biophys Acta. 2014 Feb;1843(2):352-65. doi: 10.1016/j.bbamcr.2013.11.018. Epub 2013 Dec 3.
Alpha-synuclein is a small protein implicated in the pathophysiology of Parkinson's disease (PD). We have investigated the mechanism of cleavage of alpha-synuclein by the 20S proteasome. Alpha-synuclein interacts with the C8 (α7) subunit of the proteasome. The N-terminal part of alpha-synuclein (amino acids 1-60) is essential for its proteasomal degradation and analysis of peptides released from proteasomal digestion allows concluding that initial cleavages occur within the N-terminal region of the molecule. Aggregated alpha-synucleins are also degraded by the proteasome with a reduced rate, likely due to Met oxidation. In fact, mild oxidation of alpha-synuclein with H2O2 resulted in the inhibition of its degradation by the proteasome, mainly due to oxidation of Met 1 and 5 of alpha-synuclein. The inhibition was reversed by treatment of the oxidized protein with methionine sulfoxide reductases (MsrA plus MsrB). Similarly, treatment with H2O2 of N2A cells transfected with alpha-synuclein resulted in the inhibition of its degradation that was also reverted by co-transfection of MsrA plus MsrB. These results clearly indicate that oxidative stress, a common feature of PD and other synucleinopathies, promotes a RedOx change in the proteostasis of alpha-synuclein due to Met oxidation and reduced proteasomal degradation; compromised reversion of those oxidative changes would result in the accumulation of oxidative damaged alpha-synuclein likely contributing to the pathogenesis of PD.
α-突触核蛋白是一种与帕金森病（PD）病理生理学相关的小蛋白。我们研究了20S蛋白酶体切割α-突触核蛋白的机制。α-突触核蛋白与蛋白酶体的C8（α7）亚基相互作用。α-突触核蛋白的N端部分（氨基酸1-60）对其蛋白酶体降解至关重要，对蛋白酶体消化释放的肽段进行分析可得出结论，初始切割发生在分子的N端区域内。聚集的α-突触核蛋白也能被蛋白酶体降解，但速率降低，这可能是由于甲硫氨酸氧化所致。事实上，用H2O2对α-突触核蛋白进行轻度氧化会导致其被蛋白酶体降解受到抑制，主要原因是α-突触核蛋白的甲硫氨酸1和5发生了氧化。用甲硫氨酸亚砜还原酶（MsrA加MsrB）处理氧化蛋白可逆转这种抑制作用。同样，用H2O2处理转染了α-突触核蛋白的N2A细胞会导致其降解受到抑制，而共转染MsrA加MsrB也可逆转这种抑制作用。这些结果清楚地表明，氧化应激是PD和其他突触核蛋白病的一个共同特征，由于甲硫氨酸氧化和蛋白酶体降解减少，它促进了α-突触核蛋白蛋白质稳态的氧化还原变化；这些氧化变化的逆转受损将导致氧化损伤的α-突触核蛋白积累，这可能有助于PD的发病机制。
