Pirmoradian Mohammad, Aarsland Dag, Zubarev Roman A
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Biomotif AB, Stockholm, Sweden.
Discoveries (Craiova). 2016 Dec 1;4(4):e67. doi: 10.15190/d.2016.14.
Theoretical distribution of isoelectric points (pI values) of human blood proteins exhibits multi-modality with a deep minimum in the range between pI 7.30 and 7.50. Considering that the pH of human blood is 7.4±0.1, normal forms of human proteins tend to eschew this specific pI region, thus avoiding charge neutrality that can result in enhanced precipitation. However, abnormal protein isoforms (proteoforms), which are the hallmarks and potential biomarkers of certain diseases, are likely to be found everywhere in the pI distribution, including this "forbidden" region. Therefore, we hypothesized that damaging proteoforms characteristic for neurodegenerative diseases are best detected around pI≈7.4. Blood serum samples from 14 Alzheimer's disease patients were isolated by capillary isoelectric focusing and analyzed by liquid chromatography hyphenated with tandem mass spectrometry. Consistent with the pI≈7.4 hypothesis, the 8 patients with fast memory decline had a significantly (p<0.003) higher concentration of proteoforms in the pI=7.4±0.1 region than the 6 patients with a slow memory decline. Moreover, protein compositions differed more from each other than for any other investigated pI region, providing absolute separation of the fast and slow decliner samples. The discovery of the "treasure island" of abnormal proteoforms in form of the pI≈7.4 region promises to boost biomarker development for a range of diseases.
人类血液蛋白质等电点（pI值）的理论分布呈现多峰性，在pI 7.30至7.50范围内有一个明显的最小值。考虑到人类血液的pH值为7.4±0.1，人类蛋白质的正常形式倾向于避开这个特定的pI区域，从而避免可能导致沉淀增强的电荷中性。然而，异常蛋白质异构体（蛋白变体）是某些疾病的标志和潜在生物标志物，可能在pI分布的任何地方被发现，包括这个“禁区”。因此，我们假设神经退行性疾病特有的损伤性蛋白变体在pI≈7.4附近最容易被检测到。通过毛细管等电聚焦分离了14名阿尔茨海默病患者的血清样本，并通过液相色谱-串联质谱联用进行分析。与pI≈7.4的假设一致，8名记忆衰退迅速的患者在pI = 7.4±0.1区域的蛋白变体浓度显著（p<0.003）高于6名记忆衰退缓慢的患者。此外，蛋白质组成彼此之间的差异比其他任何研究的pI区域都大，实现了快速衰退者和缓慢衰退者样本的绝对分离。以pI≈7.4区域形式发现异常蛋白变体的“宝岛”有望推动一系列疾病的生物标志物开发。
