Maccarana Marco, Olander Benny, Malmström Johan, Tiedemann Kerstin, Aebersold Ruedi, Lindahl Ulf, Li Jin-Ping, Malmström Anders
Department of Experimental Medical Science, Lund University, BMC C13, SE-221 84 Lund, Sweden.
J Biol Chem. 2006 Apr 28;281(17):11560-8. doi: 10.1074/jbc.M513373200. Epub 2006 Feb 27.
We identified the gene encoding chondroitin-glucuronate C5-epimerase (EC 5.1.3.19) that converts D-glucuronic acid to L-iduronic acid residues in dermatan sulfate biosynthesis. The enzyme was solubilized from bovine spleen, and an approximately 43,000-fold purified preparation containing a major 89-kDa candidate component was subjected to mass spectrometry analysis of tryptic peptides. SART2 (squamous cell carcinoma antigen recognized by T cell 2), a protein with unknown function highly expressed in cancer cells and tissues, was identified by 18 peptides covering 26% of the sequence. Transient expression of cDNA resulted in a 22-fold increase in epimerase activity in 293HEK cell lysate. Moreover, overexpressing cells produced dermatan sulfate chains with 20% of iduronic acid-containing disaccharide units, as compared with 5% for mock-transfected cells. The iduronic acid residues were preferentially clustered in blocks, as in naturally occurring dermatan sulfate. Given the discovered identity, we propose to rename SART2 (Nakao, M., Shichijo, S., Imaizumi, T., Inoue, Y., Matsunaga, K., Yamada, A., Kikuchi, M., Tsuda, N., Ohta, K., Takamori, S., Yamana, H., Fujita, H., and Itoh, K. (2000) J. Immunol. 164, 2565-2574) with a functional designation, chondroitin-glucuronate C5-epimerase (or DS epimerase). DS epimerase activity is ubiquitously present in normal tissues, although with marked quantitative differences. It is highly homologous to part of the NCAG1 protein, encoded by the C18orf4 gene, genetically linked to bipolar disorder. NCAG1 also contains a putative chondroitin sulfate sulfotransferase domain and thus may be involved in dermatan sulfate biosynthesis. The functional relation between dermatan sulfate and cancer is unknown but may involve known iduronic acid-dependent interactions with growth factors, selectins, cytokines, or coagulation inhibitors.
我们鉴定出了编码硫酸皮肤素生物合成过程中催化D-葡萄糖醛酸转化为L-艾杜糖醛酸残基的软骨素-葡萄糖醛酸C5-表异构酶（EC 5.1.3.19）的基因。该酶从牛脾脏中溶解出来，对一种含有主要89 kDa候选成分的约43,000倍纯化制剂进行了胰蛋白酶肽段的质谱分析。通过覆盖26%序列的18个肽段鉴定出了SART2（T细胞识别的鳞状细胞癌抗原2），一种在癌细胞和组织中高表达但功能未知的蛋白质。cDNA的瞬时表达导致293HEK细胞裂解物中的表异构酶活性增加了22倍。此外，与mock转染细胞中5%的含艾杜糖醛酸二糖单元相比，过表达细胞产生的硫酸皮肤素链含有20%的含艾杜糖醛酸二糖单元。艾杜糖醛酸残基优先聚集形成块状，如同天然存在的硫酸皮肤素一样。鉴于已发现的一致性，我们建议将SART2（中尾，M.，七条，S.，今泉，T.，井上，Y.，松永，K.，山田，A.，菊池，M.，津田，N.，太田，K.，高森，S.，山中，H.，藤田，H.，及伊藤，K.（2000年）《免疫学杂志》164，2565 - 2574）重新命名为具有功能名称的软骨素-葡萄糖醛酸C5-表异构酶（或DS表异构酶）。DS表异构酶活性普遍存在于正常组织中，尽管存在明显的数量差异。它与由C18orf4基因编码的NCAG1蛋白的一部分高度同源，该基因与双相情感障碍存在遗传关联。NCAG1还包含一个假定的硫酸软骨素磺基转移酶结构域，因此可能参与硫酸皮肤素的生物合成。硫酸皮肤素与癌症之间的功能关系尚不清楚，但可能涉及已知的与生长因子、选择素、细胞因子或凝血抑制剂的艾杜糖醛酸依赖性相互作用。
