Direct Determination of the Site of Addition of Glucosyl Units to Maltooligosaccharide Acceptors Catalyzed by Maize Starch Synthase I.
Direct Determination of the Site of Addition of Glucosyl Units to Maltooligosaccharide Acceptors Catalyzed by Maize Starch Synthase I.
复制标题
直接确定将葡萄糖基单元添加到由玉米淀粉合酶I催化的麦芽糖糖类受体中的位点。
DOI：
10.3389/fpls.2018.01252
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发表时间：
2018
影响因子：
5.6
通讯作者：
Myers AM
中科院分区：
文献类型：
--
作者：
Xie Y;Barb AW;Hennen-Bierwagen TA;Myers AM
淀粉合成酶（ADP-glucose:1,4-α- d -葡聚糖4-α- d -葡萄糖基转移酶）在质体内拉长α-（1→4）链链葡聚糖，生成构成淀粉颗粒的储存聚合物。多个SS类在整个植物界都是保守的，这表明每个SS类都有一个独特的功能，负责进化选择。有证据表明ADPglucose供体在受体底物的还原端或非还原端添加了葡萄糖基单位，尽管直到最近才有直接证据解决这个问题。新加入葡萄糖基单位的鉴定确定重组玉米（Zea mays L.）siia在非还原端拉长其底物。然而，其他SSs可能利用不同的机制，并且一种或多种保守酶类可以在还原端延长受体，这种可能性仍然存在。本研究对重组玉米SSI的反应机理及其加成位点进行了研究。新加入的残基用13C标记，延伸产物的还原端用化学衍生化标记。电喷雾电离串联质谱法测得新加入的残渣和还原端两个参数。结果表明，SSI在非还原端延长葡聚糖。该研究还证实了先前的研究结果，即重组SSI可以产生至少25个单位的葡聚糖，它在短如麦芽糖的受体中具有活性，重组形式的酶绝对需要一个受体才能具有活性，并且它不能与低麦芽糖受体底物饱和。
Starch synthase (SS) (ADP-glucose:1,4-α-D-glucan 4-α-D-glucosyltransferase) elongates α-(1→4)-linked linear glucans within plastids to generate the storage polymers that constitute starch granules. Multiple SS classes are conserved throughout the plant kingdom, indicating that each provides a unique function responsible for evolutionary selection. Evidence has been presented arguing for addition of glucosyl units from the ADPglucose donor to either the reducing end or the non-reducing end of the acceptor substrate, although until recently direct evidence addressing this question was not available. Characterization of newly incorporated glucosyl units determined that recombinant maize (Zea mays L.) SSIIa elongates its substrates at the non-reducing end. However, the possibility remained that other SSs might utilize distinct mechanisms, and that one or more of the conserved enzyme classes could elongate acceptors at the reducing end. This study characterized the reaction mechanism of recombinant maize SSI regarding its addition site. Newly incorporated residues were labeled with 13C, and reducing ends of the elongation products were labeled by chemical derivitization. Electrospray ionization-tandem mass spectroscopy traced the two parameters, i.e., the newly added residue and the reducing end. The results determined that SSI elongates glucans at the non-reducing end. The study also confirmed previous findings showing recombinant SSI can generate glucans of at least 25 units, that it is active using acceptors as short as maltotriose, that recombinant forms of the enzyme absolutely require an acceptor for activity, and that it is not saturable with maltooligosaccharide acceptor substrates.
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影响因子：
4.8
作者：
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通讯作者：
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