Clinical Neurochemistry Laboratory, Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.
J Mass Spectrom. 2012 May;47(5):591-603. doi: 10.1002/jms.2987.
Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low-energy collision-induced dissociation tandem mass spectrometry (MS/MS), mainly long b-fragments are observed, limiting the possibility to determine variations such as amino acid variants or post-translational modifications (PTMs) within the N-terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann-Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O-glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top-down MS-based method.
淀粉样前体蛋白（APP）是淀粉样β（Aβ）的前体蛋白，是阿尔茨海默病（AD）老年斑的主要成分。内源性 Aβ 肽反映了 APP 的加工，了解不同的 APP 降解途径的更多知识对于理解 AD 病理机制很重要。当通过低能量碰撞诱导解离串联质谱（MS/MS）分析较长的 Aβ 肽时，主要观察到长 b-片段，限制了在肽的 N 端半部分确定氨基酸变体或翻译后修饰（PTM）等变化的可能性。然而，通过使用电子俘获解离（ECD），我们获得了几种 APP/Aβ 肽的更全面的序列覆盖，从而能够更深入地表征可能的变体和 PTM。溶酶体贮积病尼曼-皮克 C 型中也描述了异常的 APP/Aβ 加工，用于研究这种疾病的主要大型动物是猫。通过 ECD MS/MS，鉴定出猫 Aβ 中 Asp7→Glu 的取代。此外，还在猫脑脊液（CSF）中鉴定到了 Tyr10 处的唾液酸化核心 1 样 O-聚糖，该聚糖最近在人类 Aβ 中发现（一种以前未知的糖基化类型）。因此，这种不寻常的糖基化类型很可能在（至少）属于巨核动物界的物种中普遍存在。我们在这里描述了一种通过在线自上而下的基于 MS 的方法对 CSF 中内源性 APP/Aβ 肽的详细特征进行描述。
