Modulation of Ligand Binding Affinity of Tumorigenic Carbonic Anhydrase XII upon Interaction with Cationic CdTe Quantum Dots.
Modulation of Ligand Binding Affinity of Tumorigenic Carbonic Anhydrase XII upon Interaction with Cationic CdTe Quantum Dots.
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DOI：
10.1166/jbn.2008.009
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发表时间：
2008-12-01
影响因子：
2.9
通讯作者：
Srivastava DK
中科院分区：
文献类型：
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作者：
Manokaran S;Berg A;Zhang X;Chen W;Srivastava DK
致瘤性碳酸酐酶(CA)XII的结构数据表明，活性部位口袋对面的酶表面带负电荷，因此它有可能与带正电荷的表面相互作用。我们考察了阳离子CdTe量子点对酶的催化和配体结合性能的影响。虽然阳离子量子点与CAXⅡ相互作用(Kd值为2.1μM)，但它们不影响酶的催化活性，表明酶活性部位的可及性不受上述相互作用的影响。当用阳离子量子点滴定CAXII结合的丹磺酰胺(既是酶的荧光探针又是酶的有效抑制剂)时，荧光光谱表明上述物种之间的激发态能量发生了显著的转移。然而，量子点与CAXII的结合削弱了丹磺酰胺对该酶的亲和力，从而消除了该配体的抑制作用。由于量子点和丹磺酰胺结合在CAXII的相反侧，它们的影响必须通过变构酶观察到的远端蛋白质构象的变化来调节。从这些研究中获得的机械性见解可能会导致开发致瘤CAXII的诊断方案。
The structural data of tumorigenic carbonic anhydrase (CA) XII revealed that the enzyme surface opposite to the active site pocket was negatively charged, and thus it had potential to interact with the positively charged surfaces. We investigated the influence of cationic CdTe quantum dots on the catalytic and ligand binding properties of the enzyme. Although cationic quantum dots interacted with CAXII (with a Kd value of 2.1 μM), they did not impair the enzyme’s catalytic activity, suggesting that the accessibility of the enzyme’s active site remained unaffected by the above interaction. When CAXII bound dansylamide (serving as a fluorescence probe as well as a potent inhibitor of the enzyme) was titrated with cationic quantum dots, the fluorescence spectral profiles revealed a marked transfer of the excited state energy between the above species. However, the binding of quantum dots to CAXII weakened the affinity of dansylamide for the enzyme, and thus obviated the inhibitory feature of the ligand. Since the quantum dots and dansylamide are bound at the opposite sides of CAXII, their influence must be mediated via changes in the protein conformation at a distal region as observed with allosteric enzymes. The mechanistic insights gained from these studies may lead toward developing diagnostic protocols for tumorigenic CAXII.