Core Glycosylation of Collagen Is Initiated by Two β(1-O)Galactosyltransferases
Core Glycosylation of Collagen Is Initiated by Two β(1-O)Galactosyltransferases
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DOI：
10.1128/mcb.02085-07
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发表时间：
2009-02-15
影响因子：
5.3
通讯作者：
Hennet, Thierry
中科院分区：
文献类型：
--
作者：
Schegg, Belinda;Huelsmeier, Andreas J.;Hennet, Thierry
胶原蛋白是三个左手 α 链的三聚体，代表重复的 Gly-X-Y 基序，其中（羟基）脯氨酸和（羟基）赖氨酸残基经常出现在 X 和 Y 位。选定的羟基赖氨酸通过添加半乳糖和葡萄糖-半乳糖单元进行进一步修饰。胶原糖基化发生在三螺旋形成之前的内质网中，并由 β(1-O) 半乳糖基转移酶和 α(1-2) 葡萄糖基转移酶介导。我们使用亲和色谱和串联质谱蛋白质测序鉴定了两种胶原半乳糖基转移酶。两种胶原蛋白 β(1-O) 半乳糖基转移酶对应于 GLT25D1 和 GLT25D2 蛋白。重组 GLT25D1 和 GLT25D2 酶对各种类型的胶原蛋白和血清甘露糖结合凝集素 MBL（包含胶原蛋白结构域）表现出强大的半乳糖基转移酶活性。 GLT25D1和GLT25D2反应产物的氨基酸分析证实了半乳糖向羟赖氨酸残基的转移。 GLT25D1基因在人体组织中组成型表达，而GLT25D2基因仅在神经系统中低水平表达。 GLT25D1 和 GLT25D2 酶与 CEECAM1 相似，我们无法将任何胶原半乳糖基转移酶活性归因于 CEECAM1。 GLT25D1 和 GLT25D2 基因现在可以解决胶原蛋白糖基化的生物学意义以及这种翻译后修饰在结缔组织疾病病因学中的重要性。
Collagen is a trimer of three left-handed alpha chains representing repeats of the motif Gly-X-Y, where (hydroxy) proline and (hydroxy) lysine residues are often found at positions X and Y. Selected hydroxylysines are further modified by the addition of galactose and glucose-galactose units. Collagen glycosylation takes place in the endoplasmic reticulum before triple-helix formation and is mediated by beta(1-O) galactosyl- and alpha(1-2) glucosyltransferase enzymes. We have identified two collagen galactosyltransferases using affinity chromatography and tandem mass spectrometry protein sequencing. The two collagen beta(1-O) galactosyltransferases corresponded to the GLT25D1 and GLT25D2 proteins. Recombinant GLT25D1 and GLT25D2 enzymes showed a strong galactosyltransferase activity toward various types of collagen and toward the serum mannose-binding lectin MBL, which contains a collagen domain. Amino acid analysis of the products of GLT25D1 and GLT25D2 reactions confirmed the transfer of galactose to hydroxylysine residues. The GLT25D1 gene is constitutively expressed in human tissues, whereas the GLT25D2 gene is expressed only at low levels in the nervous system. The GLT25D1 and GLT25D2 enzymes are similar to CEECAM1, to which we could not attribute any collagen galactosyltransferase activity. The GLT25D1 and GLT25D2 genes now allow addressing of the biological significance of collagen glycosylation and the importance of this posttranslational modification in the etiology of connective tissue disorders.