Basu Anirban, Suresh Kumar Gopinatha
Biophysical Chemistry Laboratory, Organic & Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India.
Mol Biosyst. 2017 Jul 25;13(8):1552-1564. doi: 10.1039/c7mb00207f.
The binding of the common food colorant carmoisine and its inhibitory effect on amyloid fibrillation in lysozyme have been investigated. Since humans are increasingly exposed to various food colorants like carmoisine, such studies are highly relevant. In the presence of lysozyme, the carmoisine absorption spectrum exhibited hypochromic changes. The intrinsic fluorescence of lysozyme was also quenched on interaction. Time-resolved fluorescence results suggested that the binding mechanism involved ground state complexation. The binding was predominantly dominated by non-polyelectrolytic forces. The molecular distance between the donor (lysozyme) and the acceptor (carmoisine), calculated from FRET theory, was found to be 3.37 nm, indicating that carmoisine binds close to Trp-62/63 residues in the β-domain of the protein. Information on alterations in the microenvironment surrounding the Trp-residues was also obtained from synchronous fluorescence data. Carmoisine binding induced significant loss in the alpha helical organization of lysozyme. The binding, nevertheless, did not influence the thermal stability of lysozyme significantly. The binding reaction was exothermic and driven by large negative enthalpy and small but favourable entropic contributions. Thioflavin T assay, far-UV circular dichroism studies and AFM imaging profiles testified that carmoisine had a significant inhibitory effect on amyloid fibrillogenesis in lysozyme. Carmoisine also had a definitive defibrillating effect on existing fibrils. The results may provide new insights for designing new small molecule inhibitors for amyloid related diseases.
对常见食用色素胭脂红的结合及其对溶菌酶淀粉样纤维化的抑制作用进行了研究。由于人类越来越多地接触到各种食用色素，如胭脂红，此类研究具有高度相关性。在溶菌酶存在的情况下，胭脂红吸收光谱呈现减色变化。溶菌酶的固有荧光在相互作用时也发生猝灭。时间分辨荧光结果表明，结合机制涉及基态络合。结合主要由非聚电解质力主导。根据荧光共振能量转移（FRET）理论计算，供体（溶菌酶）和受体（胭脂红）之间的分子距离为3.37 nm，这表明胭脂红靠近蛋白质β结构域中的Trp-62/63残基结合。从同步荧光数据中还获得了有关Trp残基周围微环境变化的信息。胭脂红结合导致溶菌酶的α螺旋结构显著丧失。然而，这种结合并未显著影响溶菌酶的热稳定性。结合反应是放热的，由大的负焓和小但有利的熵贡献驱动。硫黄素T测定、远紫外圆二色性研究和原子力显微镜成像图谱证明，胭脂红对溶菌酶中的淀粉样纤维形成具有显著的抑制作用。胭脂红对现有纤维也具有明确的解纤作用。这些结果可能为设计针对淀粉样相关疾病的新型小分子抑制剂提供新的见解。
