Synthesis and structural characterization of the peptide epitope of the ovarian cancer biomarker CA125 (MUC16)
Synthesis and structural characterization of the peptide epitope of the ovarian cancer biomarker CA125 (MUC16)
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DOI：
10.1007/s13277-010-0062-4
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发表时间：
2010-10-01
期刊：
影响因子：
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通讯作者：
Whelan, Rebecca J.
中科院分区：
文献类型：
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作者：
Berman, Zach T.;Moore, Lee J.;Whelan, Rebecca J.
一个高度保守的21个氨基酸的区域，两侧是半胱氨酸残基，包含在一个更大的重复结构域，已被提出是卵巢癌生物标志物CA 125（MUC 16）中的抗体结合位点。在本研究中，使用Fmoc保护化学的固相肽合成来组装对应于CA 125中最常见的抗体结合序列的21-mer肽。还合成了潜在重要的序列变体。肽的二级结构进行了研究，使用傅里叶变换红外光谱，揭示了共识序列肽在生理pH值下，无论半胱氨酸残基被还原或被氧化，形成分子内二硫键，在很大程度上是非结构化的。在位置8（P8 S）处丝氨酸取代脯氨酸导致参与分子内二硫键的肽中的β-折叠形成。这种β-折叠结构在由于序列而不能形成分子内二硫键的肽中不存在，在用还原剂二硫苏糖醇处理的肽中也不存在。在CA 125中，预测P8 S发生在类似于25%的重复结构域中，表明该结构基序对整体结构和功能是不可忽略的贡献者。这些发现表明，未来CA 125的结构表征工作应特别注意蛋白质的氨基酸序列和氧化态。
A highly conserved region of 21 amino acids flanked by cysteine residues, contained within a larger repeated domain, has been proposed to be the antibody-binding site in the ovarian cancer biomarker CA125 (MUC16). In this study solid-phase peptide synthesis with Fmoc protection chemistry was used to assemble a 21-mer peptide corresponding to the most frequently occurring antibody binding sequence in CA125. Potentially significant sequence variants were also synthesized. Peptide secondary structure was investigated using Fourier transform infrared spectroscopy, revealing the consensus sequence peptide to be largely unstructured at physiological pH whether the cysteine residues were reduced or were oxidized to form an intramolecular disulfide bond. Substitution of serine for proline at position 8 (P8S) results in beta-sheet formation in peptides involved in intramolecular disulfide bonds. This beta-sheet structure does not persist in peptides incapable of intramolecular disulfide bonding because of sequence nor in peptides treated with the reducing agent dithiothreitol. In CA125, P8S is predicted to occur in similar to 25% of repeat domains, suggesting that this structural motif is a non-negligible contributor to overall structure and function. These findings suggest that future structural characterization efforts of CA125 should be especially mindful of the amino acid sequence and oxidation state of the protein.