The design, synthesis and evaluation of high affinity macrocyclic carbohydrate inhibitors
作者:Robert S. McGavin、Rod A. Gagne、Mary C. Chervenak、David R. Bundle
DOI:10.1039/b416105j
日期:——
Carbohydrate–protein interactions have been investigated for a model system of a monoclonal antibody, SYA/J6, which binds a trisaccharide epitope of the O-polysaccharide of the Shigella flexneri variant Y lipopolysaccharide. The thermodynamics of binding for the methyl glycoside of the native trisaccharide epitope, Rha-Rha-GlcNAc (1) to SYA/J6 over a range of temperatures exhibits strong, linear enthalpy–entropy compensation and a negative heat capacity change (ΔCp
=
−152 cal mol−1 degree−1). At 293 K the free energy of association is the sum of favourable enthalpy and entropy contributions (ΔH
=
−3.9 kcal mol−1 and −TΔS
=
−2.9 kcal mol−1). Crystal structures for SYA/J6 Fab detailed the position of the native trisaccharide epitope, Rha-Rha-GlcNAc (1), and facilitated a strategy to design a tighter binding, low molecular weight ligand. This involved pre-organization of the native trisaccharide 1 in its bound conformation by addition of intramolecular constraints (a β-alanyl or glycinyl tether). ELISA measurements indicated that the glycinyl tethered trisaccharide 2 was not an optimal candidate for further analysis, while microcalorimetry provided data showing that the β-alanyl tethered trisaccharide 3 displayed a 15-fold increase in affinity for SYA/J6. Tethering of 3 resulted in a favourable entropic contribution to binding, relative to the native trisaccharide 1
(−TΔΔS
=
−1.2 kcal mol−1). Potential energy and dynamics calculations using the AMBER Plus force fields indicated that trisaccharide 3 adopted a rigid conformation similar to that of the bound conformation of the native trisaccharide epitope. While this strategy resulted in modest free energy gains by minimizing losses due to conformational entropy, thermodynamic data are consistent with significant contributions from solvent reorganization.
碳水化合物-蛋白质相互作用已针对一种单克隆抗体模型系统 SYA/J6 进行了研究,该抗体结合了志贺氏杆菌柔性 Y 型脂多糖 O-多糖的三糖表位。天然三糖表位的甲基糖苷(Rha-Rha-GlcNAc,1)与 SYA/J6 在不同温度下的结合热力学表现为强烈的线性焓-熵补偿和负热容变化(ΔCp = -152 卡/摩尔/度)。在 293 K 时,结合自由能是焓和熵的有利贡献之和(ΔH = -3.9 千卡/摩尔,-TΔS = -2.9 千卡/摩尔)。SYA/J6 Fab 的晶体结构详细描述了天然三糖表位 Rha-Rha-GlcNAc(1)的位置,并促成了一种策略,即设计一种更紧密结合的低分子量配体。这一策略包括通过添加内分子约束(β-丙氨酸或甘氨酸接头)使天然三糖 1 在其结合构象中预排列。ELISA 测量表明,甘氨酸接头的三糖 2 不是进一步分析的理想候选物,而微量热法数据显示,β-丙氨酸接头的三糖 3 对 SYA/J6 的亲和力提高了 15 倍。与天然三糖 1 相比,3 的接头导致了对结合有利的熵贡献(-TΔΔS = -1.2 千卡/摩尔)。使用 AMBER Plus 力场进行的势能和动力学计算表明,三糖 3 采取了类似于天然三糖表位结合构象的刚性构象。尽管这种策略通过最小化构象熵损失实现了适度的自由能增益,但热力学数据与溶剂重组的大量贡献是一致的。