Poly-N-acetyllactosamine is a unique carbohydrate that can carry various functional oligosaccharides, such as sialyl Lewis X. It has been shown that the amount of poly-N-acetyllactosamine is increased in N-glycans, when they contain Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->4GlcNAcbeta1 -->2)Manalpha1-->6 branched structure. To determine how this increased synthesis of poly-N-acetyllactosamines takes place, the branched acceptor was incubated with a mixture of i-extension enzyme (iGnT) and beta1, 4galactosyltransferase I (beta4Gal-TI). First, N-acetyllactosamine repeats were more readily added to the branched acceptor than the summation of poly-N-acetyllactosamines formed individually on each unbranched acceptor. Surprisingly, poly-N-acetyllactosamine was more efficiently formed on Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chain than in Galbeta1-->4GlcNAcbeta1-->6Manalpha-->R, due to preferential action of iGnT on Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chain. On the other hand, galactosylation was much more efficient on beta1,6-linked GlcNAc than beta1,2-linked GlcNAc, preferentially forming Galbeta1-->4GlcNAcbeta1-->6(GlcNAcbeta1-->2)Manalph a1-->6Manbeta -->R. Starting with this preformed acceptor, N-acetyllactosamine repeats were added almost equally to Galbeta1-->4GlcNAcbeta1-->6Manalpha-->R and Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chains. Taken together, these results indicate that the complemental branch specificity of iGnT and beta4Gal-TI leads to efficient and equal addition of N-acetyllactosamine repeats on both side chains of GlcNAcbeta1-->6(GlcNAcbeta1-->2)Manalpha1-->6Manbet a-->R structure, which is consistent with the structures found in nature. The results also suggest that the addition of Galbeta1-->4GlcNAcbeta1-->6 side chain on Galbeta1-->4GlcNAcbeta1-->2Man-->R side chain converts the acceptor to one that is much more favorable for iGnT and beta4Gal-TI.

中文翻译：

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支链N-聚糖中的聚-N-乙酰基乳糖胺合成受I-延伸酶和β1,4-半乳糖基转移酶I的互补支链特异性控制。

聚-N-乙酰基乳糖胺是一种独特的碳水化合物，可以携带各种功能性低聚糖，例如唾液酸路易斯X。当N-聚糖中含有Galbeta1-> 4GlcNAcbeta1时，聚-N-乙酰基乳糖胺的含量会增加。 -> 6（Galbeta1-> 4GlcNAcbeta1-> 2）Manalpha1-> 6分支结构。为了确定这种增加的聚-N-乙酰基乳糖胺的合成是如何发生的，将支链受体与i-延伸酶（iGnT）和beta1，4-半乳糖基转移酶I（beta4Gal-TI）的混合物孵育。首先，与在每个非支链受体上单独形成的聚-N-乙酰基乳糖胺的总和相比，更容易将N-乙酰基乳糖胺重复序列添加至支链受体。出人意料的是，在Galbeta1-> 4GlcNAcbeta1-> 2Manalpha->上更有效地形成了聚N-乙酰基乳糖胺 由于iGnT对Galbeta1-> 4GlcNAcbeta1-> 2Manalpha-> ​​R侧链的优先作用，R侧链比Galbeta1-> 4GlcNAcbeta1-> 6Manalpha-> ​​R中的高。另一方面，与β1,2-连接的GlcNAc相比，与β1,6-连接的GlcNAc的半乳糖基化效率更高，优先形成Galbeta1-> 4GlcNAcbeta1-> 6（GlcNAcbeta1-> 2）Manalph a1-> 6Manbeta- -> R。从此预先形成的受体开始，N-乙酰基乳糖胺重复序列几乎均等地添加到Galbeta1-> 4GlcNAcbeta1-> 6Manalpha-> ​​R和Galbeta1-> 4GlcNAcbeta1-> 2Manalpha-> ​​R侧链上。综上所述，这些结果表明，iGnT和beta4Gal-TI的互补分支特异性导致在GlcNAcbeta1-> 6（GlcNAcbeta1-> 2）Manalpha1->的两个侧链上有效且相等地添加N-乙酰基乳糖胺重复序列。6Manbet a-> R结构，与自然界中发现的结构一致。结果还表明，在Galbeta1-> 4GlcNAcbeta1-> 2Man-> R侧链上添加Galbeta1-> 4GlcNAcbeta1-> 6侧链可将受体转变为对iGnT和beta4Gal-更有利的受体TI。