Doucey M A, Hess D, Blommers M J, Hofsteenge J
Friedrich Miescher-Institut, P.O. Box 2543, CH-4002 Basel, Switzerland.
Glycobiology. 1999 May;9(5):435-41. doi: 10.1093/glycob/9.5.435.
The beta-chain of human interleukin 12 (IL-12) contains at position 319-322, the sequence Trp-x-x-Trp. In human RNase 2 this is the recognition motif for a new, recently discovered posttranslational modification, i.e., the C-glycosidic attachment of a mannosyl residue to the side chain of tryptophan. Analysis of C-terminal peptides of recombinant IL-12 (rHuIL-12) by mass spectrometry and NMR spectroscopy revealed that Trp-319beta is (partially) C-mannosylated. This finding was extended by in vitro mannosylation experiments, using a synthetic peptide derived from the same region of the protein as an acceptor. Furthermore, human B-lymphoblastoid cells, which secrete IL-12, were found to contain an enzyme that carries out the C-mannosylation reaction. This shows that nonrecombinant IL-12 is potentially C-mannosylated as well. This is only the second report on a C-mannosylated protein. However, the occurrence of the C-mannosyltransferase activity in a variety of cells and tissues, and the presence of the recognition motif in many proteins indicate that more C-mannosylated proteins may be found.
人白细胞介素12（IL-12）的β链在第319 - 322位包含序列Trp-x-x-Trp。在人核糖核酸酶2中，这是一种新的、最近发现的翻译后修饰的识别基序，即甘露糖基残基以C-糖苷键形式连接到色氨酸侧链上。通过质谱和核磁共振光谱对重组IL-12（rHuIL-12）的C末端肽段进行分析，结果显示Trp-319β（部分）被C-甘露糖基化。使用源自该蛋白相同区域的合成肽作为受体进行的体外甘露糖基化实验进一步证实了这一发现。此外，发现分泌IL-12的人B淋巴母细胞含有一种能进行C-甘露糖基化反应的酶。这表明非重组IL-12也可能被C-甘露糖基化。这是关于C-甘露糖基化蛋白的第二篇报道。然而，多种细胞和组织中存在C-甘露糖基转移酶活性，且许多蛋白质中存在识别基序，这表明可能会发现更多的C-甘露糖基化蛋白。
