Department of Clinical Chemistry and Transfusion Medicine, Institute of Biomedicine, University of Gothenburg, SE-413 45 Gothenburg, Sweden.
Proc Natl Acad Sci U S A. 2011 Jul 19;108(29):11848-53. doi: 10.1073/pnas.1102664108. Epub 2011 Jun 28.
The proteolytic processing of human amyloid precursor protein (APP) into shorter aggregating amyloid β (Aβ)-peptides, e.g., Aβ1-42, is considered a critical step in the pathogenesis of Alzheimer's disease (AD). Although APP is a well-known membrane glycoprotein carrying both N- and O-glycans, nothing is known about the occurrence of released APP/Aβ glycopeptides in cerebrospinal fluid (CSF). We used the 6E10 antibody and immunopurified Aβ peptides and glycopeptides from CSF samples and then liquid chromatography-tandem mass spectrometry for structural analysis using collision-induced dissociation and electron capture dissociation. In addition to 33 unglycosylated APP/Aβ peptides, we identified 37 APP/Aβ glycopeptides with sialylated core 1 like O-glycans attached to Thr(-39, -21, -20, and -13), in a series of APP/AβX-15 glycopeptides, where X was -63, -57, -52, and -45, in relation to Asp1 of the Aβ sequence. Unexpectedly, we also identified a series of 27 glycopeptides, the Aβ1-X series, where X was 20 (DAEFRHDSGYEVHHQKLVFF), 19, 18, 17, 16, and 15, which were all uniquely glycosylated on Tyr10. The Tyr10 linked O-glycans were (Neu5Ac)(1-2)Hex(Neu5Ac)HexNAc-O- structures with the disialylated terminals occasionally O-acetylated or lactonized, indicating a terminal Neu5Acα2,8Neu5Ac linkage. We could not detect any glycosylation of the Aβ1-38/40/42 isoforms. We observed an increase of up to 2.5 times of Tyr10 glycosylated Aβ peptides in CSF in six AD patients compared to seven non-AD patients. APP/Aβ sialylated O-glycans, including that of a Tyr residue, the first in a mammalian protein, may modulate APP processing, inhibiting the amyloidogenic pathway associated with AD.
人淀粉样前体蛋白（APP）的蛋白水解加工成较短的聚集态淀粉样β（Aβ）-肽，例如 Aβ1-42，被认为是阿尔茨海默病（AD）发病机制中的关键步骤。尽管 APP 是一种众所周知的膜糖蛋白，既带有 N-聚糖又带有 O-聚糖，但目前尚不清楚脑脊液（CSF）中是否存在释放的 APP/Aβ糖肽。我们使用 6E10 抗体从 CSF 样本中免疫纯化 Aβ 肽和糖肽，然后使用液相色谱-串联质谱法进行结构分析，使用碰撞诱导解离和电子捕获解离。除了 33 个未糖基化的 APP/Aβ 肽外，我们在一系列 APP/AβX-15 糖肽中鉴定了 37 个 APP/Aβ 糖肽，其中 X 为-63、-57、-52 和-45，与 Aβ 序列中的 Asp1 相关，这些糖肽带有连接到 Thr（-39、-21、-20 和-13）的唾液酸化核心 1 样 O-聚糖。出乎意料的是，我们还鉴定了一系列 27 个糖肽，即 Aβ1-X 系列，其中 X 为 20（DAEFRHDSGYEVHHQKLVFF）、19、18、17、16 和 15，它们都在 Tyr10 上被唯一地糖基化。Tyr10 连接的 O-聚糖是（Neu5Ac）（1-2）Hex（Neu5Ac）HexNAc-O-结构，其双唾液酸化末端偶尔乙酰化或内酯化，表明末端 Neu5Acα2,8Neu5Ac 键。我们无法检测到任何 Aβ1-38/40/42 同工型的糖基化。与七名非 AD 患者相比，我们在六名 AD 患者的 CSF 中观察到 Tyr10 糖基化 Aβ 肽增加了高达 2.5 倍。APP/Aβ 唾液酸化 O-聚糖，包括第一个在哺乳动物蛋白中的 Tyr 残基，可能调节 APP 加工，抑制与 AD 相关的淀粉样形成途径。
