Department of Clinical Chemistry and Transfusion Medicine, Institute of Biomedicine, Sahlgrenska Academy at the University of Gothenburg, Sweden.
Mol Cell Proteomics. 2012 Apr;11(4):M111.013649. doi: 10.1074/mcp.M111.013649. Epub 2011 Dec 14.
Urine is a complex mixture of proteins and waste products and a challenging biological fluid for biomarker discovery. Previous proteomic studies have identified more than 2800 urinary proteins but analyses aimed at unraveling glycan structures and glycosylation sites of urinary glycoproteins are lacking. Glycoproteomic characterization remains difficult because of the complexity of glycan structures found mainly on asparagine (N-linked) or serine/threonine (O-linked) residues. We have developed a glycoproteomic approach that combines efficient purification of urinary glycoproteins/glycopeptides with complementary MS-fragmentation techniques for glycopeptide analysis. Starting from clinical sample size, we eliminated interfering urinary compounds by dialysis and concentrated the purified urinary proteins by lyophilization. Sialylated urinary glycoproteins were conjugated to a solid support by hydrazide chemistry and trypsin digested. Desialylated glycopeptides, released through mild acid hydrolysis, were characterized by tandem MS experiments utilizing collision induced dissociation (CID) and electron capture dissociation fragmentation techniques. In CID-MS(2), Hex(5)HexNAc(4)-N-Asn and HexHexNAc-O-Ser/Thr were typically observed, in agreement with known N-linked biantennary complex-type and O-linked core 1-like structures, respectively. Additional glycoforms for specific N- and O-linked glycopeptides were also identified, e.g. tetra-antennary N-glycans and fucosylated core 2-like O-glycans. Subsequent CID-MS(3), of selected fragment-ions from the CID-MS(2) analysis, generated peptide specific b- and y-ions that were used for peptide identification. In total, 58 N- and 63 O-linked glycopeptides from 53 glycoproteins were characterized with respect to glycan- and peptide sequences. The combination of CID and electron capture dissociation techniques allowed for the exact identification of Ser/Thr attachment site(s) for 40 of 57 putative O-glycosylation sites. We defined 29 O-glycosylation sites which have, to our knowledge, not been previously reported. This is the first study of human urinary glycoproteins where "intact" glycopeptides were studied, i.e. the presence of glycans and their attachment sites were proven without doubt.
尿液是一种复杂的蛋白质和废物混合物,是生物标志物发现的极具挑战性的生物液体。以前的蛋白质组学研究已经鉴定出超过 2800 种尿蛋白,但缺乏用于揭示尿糖蛋白糖基结构和糖基化位点的分析。由于主要在天冬酰胺(N-连接)或丝氨酸/苏氨酸(O-连接)残基上发现的糖基结构的复杂性,糖蛋白质组学的特征仍然很困难。我们开发了一种糖蛋白质组学方法,该方法结合了高效纯化尿糖蛋白/糖肽与互补的 MS 片段化技术进行糖肽分析。从临床样本量开始,我们通过透析消除了干扰尿化合物,并通过冻干浓缩了纯化的尿蛋白。通过酰肼化学将唾液酸化的尿糖蛋白与固体载体偶联,然后用胰蛋白酶消化。通过温和的酸水解释放去唾液酸化的糖肽,然后通过串联 MS 实验利用碰撞诱导解离(CID)和电子捕获解离碎裂技术对其进行表征。在 CID-MS(2)中,通常观察到 Hex(5)HexNAc(4)-N-Asn 和 HexHexNAc-O-Ser/Thr,分别与已知的 N-连接双天线复杂型和 O-连接核心 1 样结构一致。还鉴定了特定的 N-和 O-连接糖肽的其他糖型,例如四天线 N-聚糖和岩藻糖基核心 2 样 O-聚糖。随后,对 CID-MS(2)分析中的选定片段离子进行 CID-MS(3)分析,生成用于肽鉴定的肽特异性 b-和 y-离子。总共从 53 种糖蛋白中鉴定了 58 种 N-连接和 63 种 O-连接糖肽,涉及聚糖和肽序列。CID 和电子捕获解离技术的组合允许对 57 个假定的 O-糖基化位点中的 40 个准确识别 Ser/Thr 附着位点。我们定义了 29 个 O-糖基化位点,据我们所知,这些位点以前没有报道过。这是首次对人类尿液糖蛋白进行“完整”糖肽研究,即毫无疑问地证明了聚糖及其附着位点的存在。