Methylglyoxal (MG) is a highly reactive aldehyde spontaneously formed in human cells mainly as a by-product of glycolysis. Such endogenous metabolite reacts with proteins, nucleotides and lipids forming advanced glycation end-products (AGEs). MG binds to arginine, lysine and cysteine residues of proteins causing the formation of stable adducts that can interfere with protein function. Among the proteins affected by glycation, MG has been found to react with superoxide dismutase 1 (SOD1), a fundamental anti-oxidant enzyme that is abundantly expressed in neurons. Considering the high neuronal susceptibility to MG-induced oxidative stress, we sought to investigate by mass spectrometry and NMR spectroscopy which are the structural modifications induced on SOD1 by the reaction with MG. We show that MG reacts preferentially with the disulfide-reduced, demetallated form of SOD1, gradually causing its unfolding, and to a lesser extent, with the intermediate state of maturation – the reduced, zinc-bound homodimer – causing its gradual monomerization. These results suggest that MG could impair the correct maturation of SOD1 in vivo, thus both increasing cellular oxidative stress and promoting the cytotoxic misfolding and aggregation process of SOD1.

甲基乙二醛（MG）是在人体细胞中自发形成的高反应性醛，主要是糖酵解的副产物。这种内源性代谢产物与蛋白质，核苷酸和脂质反应，形成高级糖基化终产物（AGEs）。MG与蛋白质的精氨酸，赖氨酸和半胱氨酸残基结合，导致形成稳定的加合物，从而干扰蛋白质的功能。在受糖基化影响的蛋白质中，已发现MG与超氧化物歧化酶1（SOD1）反应，超氧化物歧化酶1是一种基本的抗氧化酶，在神经元中大量表达。考虑到神经元对MG诱导的氧化应激的高度敏感性，我们寻求通过质谱和NMR光谱进行研究，它们是与MG反应在SOD1上诱导的结构修饰。我们表明MG与二硫化物还原反应优先发生，脱金属形式的SOD1，逐渐导致其展开，并在较小程度上伴随着成熟的中间状态–还原的，与锌结合的同型二聚体–导致其逐渐单体化。这些结果表明，MG可能会损害SOD1的正确成熟。在体内，因此既增加了细胞的氧化应激，又促进了SOD1的细胞毒性错折叠和聚集过程。