The human ABO antigens are carbohydrates that differ from each other by the immunodominant sugar. The O phenotype is characterized by the absence of the A- or B-defining carbohydrate. The glycosyltransferases that create the A and B antigens share a considerable amino acid sequence and a structural homology and feature 2 series of amino acids whose exact location within the enzymes' structure cannot be determined. One series is 16 amino acids in length and probably lies next to the catalytic center, whereas less is known about the other 10-amino acid disordered loop located at the C-terminus of the protein. These "disordered" segments of amino acids can be found in other glycosyltransferases from disparate species. The precise role of these amino acids is unclear although recent evidence suggests that they are involved in substrate binding and turnover. A more complete understanding of its function will provide fundamental insights into the activity of glycosyltransferases and a potential target for novel therapeutics in the case of pathogens. In this review, we describe the nature of various disordered regions in glycosyltransferase structures from bacteria to human beings.

中文翻译：

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ABO糖基转移酶中无序环的重要性。

人ABO抗原是通过免疫优势糖彼此不同的碳水化合物。O表型的特征在于不存在定义A或B的碳水化合物。产生A和B抗原的糖基转移酶具有相当的氨基酸序列和结构同源性，并且具有2个氨基酸序列，这些氨基酸无法确定其在酶结构中的确切位置。一个序列的长度为16个氨基酸，可能紧邻催化中心，而对位于蛋白C端的其他10个氨基酸无序环的了解则较少。这些氨基酸的“无序”区段可以在来自不同物种的其他糖基转移酶中找到。这些氨基酸的确切作用尚不清楚，尽管最近的证据表明它们与底物结合和周转有关。对它的功能的更完整的了解将提供对糖基转移酶活性的基本见解，并在病原体的情况下为新疗法的潜在靶标。在这篇综述中，我们描述了从细菌到人类的糖基转移酶结构中各种无序区域的性质。