Parasuraman Ponnusamy, Murugan Veeramani, Selvin Jeyasigamani F A, Gromiha M Michael, Fukui Kazuhiko, Veluraja Kasinadar
Department of Physics, Manonmaniam Sundaranar University, Tirunelveli, 627 012, India.
J Mol Recognit. 2014 Aug;27(8):482-92. doi: 10.1002/jmr.2369.
Wheat germ agglutinin (WGA) is a plant lectin, which specifically recognizes the sugars NeuNAc and GlcNAc. Mutated WGA with enhanced binding specificity can be used as biomarkers for cancer. In silico mutations are performed at the active site of WGA to enhance the binding specificity towards sialylglycans, and molecular dynamics simulations of 20 ns are carried out for wild type and mutated WGAs (WGA1, WGA2, and WGA3) in complex with sialylgalactose to examine the change in binding specificity. MD simulations reveal the change in binding specificity of wild type and mutated WGAs towards sialylgalactose and bound conformational flexibility of sialylgalactose. The mutated polar amino acid residues Asn114 (S114N), Lys118 (G118K), and Arg118 (G118R) make direct and water mediated hydrogen bonds and hydrophobic interactions with sialylgalactose. An analysis of possible hydrogen bonds, hydrophobic interactions, total pair wise interaction energy between active site residues and sialylgalactose and MM-PBSA free energy calculation reveals the plausible binding modes and the role of water in stabilizing different binding modes. An interesting observation is that the binding specificity of mutated WGAs (cyborg lectin) towards sialylgalactose is found to be higher in double point mutation (WGA3). One of the substituted residues Arg118 plays a crucial role in sugar binding. Based on the interactions and energy calculations, it is concluded that the order of binding specificity of WGAs towards sialylgalactose is WGA3 > WGA1 > WGA2 > WGA. On comparing with the wild type, double point mutated WGA (WGA3) exhibits increased specificity towards sialylgalactose, and thus, it can be effectively used in targeted drug delivery and as biological cell marker in cancer therapeutics.
小麦胚凝集素（WGA）是一种植物凝集素，它能特异性识别唾液酸（NeuNAc）和N-乙酰葡糖胺（GlcNAc）。具有增强结合特异性的突变型WGA可作为癌症的生物标志物。在计算机上对WGA的活性位点进行突变，以增强其对唾液酸聚糖的结合特异性，并对野生型和突变型WGA（WGA1、WGA2和WGA3）与唾液酸半乳糖形成的复合物进行了20纳秒的分子动力学模拟，以研究结合特异性的变化。分子动力学模拟揭示了野生型和突变型WGA对唾液酸半乳糖的结合特异性变化以及唾液酸半乳糖的结合构象灵活性。突变的极性氨基酸残基Asn114（S114N）、Lys118（G118K）和Arg118（G118R）与唾液酸半乳糖形成直接的和水介导的氢键以及疏水相互作用。对活性位点残基与唾液酸半乳糖之间可能的氢键、疏水相互作用、总成对相互作用能以及MM-PBSA自由能计算进行分析，揭示了合理的结合模式以及水在稳定不同结合模式中的作用。一个有趣的发现是，在双点突变（WGA3）中，突变型WGA（半机械人凝集素）对唾液酸半乳糖的结合特异性更高。其中一个取代残基Arg118在糖结合中起关键作用。基于相互作用和能量计算，得出WGA对唾液酸半乳糖的结合特异性顺序为WGA3＞WGA1＞WGA2＞WGA。与野生型相比，双点突变的WGA（WGA3）对唾液酸半乳糖表现出更高的特异性，因此，它可有效地用于靶向药物递送以及作为癌症治疗中的生物细胞标志物。
