Insights into the Biosynthesis of the Vibrio cholerae Major Autoinducer CAI-1 from the Crystal Structure of the PLP-Dependent Enzyme CqsA
Insights into the Biosynthesis of the Vibrio cholerae Major Autoinducer CAI-1 from the Crystal Structure of the PLP-Dependent Enzyme CqsA
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DOI：
10.1016/j.jmb.2009.07.042
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发表时间：
2009-09-25
影响因子：
5.6
通讯作者：
Taylor, Garry L.
中科院分区：
文献类型：
--
作者：
Jahan, Nasrin;Potter, Jane A.;Taylor, Garry L.
CqsA是霍乱弧菌自身诱导物-1(CaI-1)的生物合成相关酶，是霍乱弧菌群体感应的主要诱导剂。CqsA的氨基酸序列表明它属于催化氨基酸缩合到酰基辅酶A底物上的α-羟胺合成酶家族。在这里，我们给出了CqsA的apo和plp结合的晶体结构，并确认它与二聚体α-羟胺合成酶有结构上的同源性，包括一个保守的plp结合位点。CAM的化学结构表明，二十二酰辅酶A可能是CqsA的一种底物，另一种底物可能是L苏氨酸或L-2-氨基丁酸。在PLP和L-苏氨酸存在下获得的CqsA的1.9埃分辨晶体结构揭示了一个失去L-苏氨酸侧链的外源醛胺。同样，在PLP、L-苏氨酸和癸酰-辅酶A存在下，CqsA的1.9埃分辨晶体结构显示了一个捕获的外部乙二胺中间体，这表明缩合和脱羧基步骤已经发生，L-苏氨酸侧链再次丢失。结果表明，这种侧链损失是由逆Aldol反应引起的，这一结果得到了质谱学的支持。虽然目前还没有得到以L-2-氨基丁酸和癸酰-辅酶A为底物的CqsA的结构数据，但质谱学证实了该酶反应的预期产物。推测载脂蛋白结构中的一个无序区域参与了产物的释放。虽然不确定CqsA是否能够单独合成CAM，但这些结果提示了可能的合成路线。(C)2009爱思唯尔有限公司。保留所有权利。
CqsA is an enzyme involved in the biosynthesis of cholerae autoinducer-1 (CAI-1), the major Vibrio cholerae autoinducer engaged in quorum sensing. The amino acid sequence of CqsA suggests that it belongs to the family of alpha-oxoamine synthases that catalyse the condensation of an amino acid to an acyl-CoA substrate. Here we present the apo- and PLP-bound crystal structures of CqsA and confirm that it shares structural homology with the dimeric alpha-oxoamine synthases, including a conserved PLP-binding site. The chemical structure of CAM suggests that decanoyl-CoA may be one substrate of CqsA and that another substrate may be L-threonine or L-2-aminobutyric acid. A crystal structure of CqsA at 1.9-angstrom resolution obtained in the presence of PLP and L-threonine reveals an external aldimine that has lost the L-threonine side chain. Similarly, a 1.9-angstrom-resolution crystal structure of CqsA in the presence of PLP, L-threonine, and decanoyl-CoA shows a trapped external aldimine intermediate, suggesting that the condensation and decarboxylation steps have occurred, again with loss of the L-threonine side chain. It is suggested that this side-chain loss, an observation supported by mass spectrornetry is due to a retro-aldol reaction. Although no structural data have been obtained on CqsA using L-2-aminobutyric acid and decanoyl-CoA as substrates, mass spectrometry confirms the expected product of the enzyme reaction. It is proposed that a region of structure that is disordered in the apo structure is involved in the release of product. While not confirming if CqsA alone is able to synthesize CAM, these results suggest possible synthetic routes. (C) 2009 Elsevier Ltd. All rights reserved.